This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Korean government Ministry of Science and ICT (NRF-2016R1C1B2009886).

1. Solution and cell preparation
<ol>
	<li>Solution preparation
	<ol>
		<li>For the cell culture medium, prepare medium for HeLa cell culture by adding 50 mL of fetal bovine serum (FBS) to 500 mL of Dulbecco&#8217;s Modified Eagle&#8217;s Medium (DMEM). 
		NOTE: Antibiotics can be added to the cell culture medium, but we do not use antibiotics.</li>
		<li>For the 0.1% paraformaldehyde, dissolve 4% (w/v) paraformaldehyde in 1x Phosphate-Buffered Saline (PBS) with heating on a hot plate and dilute to make 30 mL of 0.1% (v/v) paraformaldehyde by adding 1x PBS. 
		CAUTION: Perform all steps in a fume hood and be careful not to boil the paraformaldehyde solution. Protect the 0.1% solution from light and store at 4 &#176;C. Use the solution within one month. 
		NOTE: The pH of the final 0.1% (v/v) paraformaldehyde solution should be around 7.</li>
		<li>Prepare fCLIP lysis buffer: 20 mM Tris-HCl (pH 7.5), 15 mM NaCl, 10 mM EDTA, 0.5% (v/v) nonidet-p40 (NP-40), 0.1% (v/v) Triton X-100, 0.1% (v/v) sodium dodecyl sulfate (SDS), and 0.1% (w/v) sodium deoxycholate. Add triple distilled water (TDW) to 40 mL. Store at 4 &#176;C.</li>
		<li>Prepare fCLIP wash buffer: 20 mM Tris-HCl (pH 7.5), 150 mM NaCl, 10 mM EDTA, 0.1% (v/v) NP-40, 0.1% (v/v) Triton X-100, 0.1% (v/v) SDS, and 0.1% (w/v) sodium deoxycholate. Add TDW to 40 mL. Store at 4 &#176;C.</li>
		<li>Prepare 4x PK buffer: 400 mM Tris-HCl (pH 7.5), 200 mM NaCl, 40 mM EDTA, and 4% (v/v) SDS. Add TDW to 40 mL. Store at room temperature.</li>
		<li>Prepare fCLIP elution buffer: 20 mL of 4x PK buffer, 21 g of urea, and 8.5 mL of TDW. Prepare fresh.</li>
		<li>Prepare RNA elution buffer: 0.3 M NaOAc and 2% (w/v) SDS. Store at room temperature.</li>
		<li>Prepare 2x RNA loading dye: 0.025% (w/v) bromophenol blue, 0.025% (w/v) xylene cyanol, 5 mM EDTA, 0.05% (w/v) SDS, and 95% (v/v) formamide. Store at -20 &#176;C.</li>
		<li>Prepare 1x TBE buffer: 0.089 M Tris-Borate and 0.002 M EDTA. Prepare 500 mL of TBE buffer.</li>
	</ol>
	</li>
	<li>Preparation of S or M phase-arrested cells
	<ol>
		<li>Seed ~750,000 or ~1,000,000 HeLa cells for S or M phase-arrested samples, respectively. Grow cells at 37 &#176;C and 5% CO2 for 24 h.</li>
		<li>Treat the cells with 2 mM thymidine and incubate for 18 h at 37 &#176;C.</li>
		<li>Wash the cells two times with PBS. Add fresh media and incubate for 9 h at 37 &#176;C.</li>
		<li>For S phase-arrested cells, treat cells with 2 mM thymidine. For M phase-arrested cells, treat cells with 100 ng/mL nocodazole. Incubate for 15 h at 37 &#176;C and harvest cells. 
		NOTE: The homogeneity of the cell cycle samples can be checked using FACS.</li>
	</ol>
	</li>
</ol>
2. Formaldehyde cross-linking and immunoprecipitation
<ol>
	<li>Cell harvest
	<ol>
		<li>For an S phase sample, collect cells with a cell scraper and transfer into a 15 mL conical tube. For an M phase sample, tap the side of the cell culture dish to detach M phase-arrested cells and transfer them into a 15 mL conical tube. 
		NOTE: To increase the homogeneity of the M phase-arrested cells, do not use a cell scraper.</li>
		<li>Centrifuge the cells at 380 x g at room temperature for 3 min. Remove the supernatant and re-suspend with 1 mL of cold PBS and transfer into a 1.5 mL microcentrifuge tube.</li>
		<li>Centrifuge the cells at 10,000 x g at 4 &#176;C for 30 s. Remove the supernatant completely.</li>
	</ol>
	</li>
	<li>Formaldehyde crosslinking
	<ol>
		<li>Add 750 &#956;L of 0.1% paraformaldehyde for 10 min at room temperature to fix the cells.</li>
		<li>Add 250 &#956;L of 1 M glycine and incubate an additional 10 min at room temperature to quench the reaction. Centrifuge the cells at 10,000 x g at 4 &#176;C for 30 s. Remove the supernatant completely.</li>
		<li>Re-suspend with 1 mL of PBS. Centrifuge the cells at 10,000 x g at 4 &#176;C for 30 s and remove the supernatant.</li>
		<li>Re-suspend with 400 &#956;L of fCLIP lysis buffer supplemented with 0.2% (v/v) protease inhibitor and 2% (v/v) RNase inhibitor. Incubate on ice for 10 min and sonicate using an ultrasonicator.</li>
		<li>Add 11 &#956;L of 5 M NaCl to adjust NaCl concentration to ~150 mM. Vortex briefly and centrifuge at 21,130 x g at 4 &#176;C for 15 min. Transfer the supernatant to a pre-chilled 1.5 mL microcentrifuge tube. 
		NOTE: Retain 40 &#956;L of supernatant in a new centrifuge tube as the input sample. Store the input sample at 4 &#176;C.</li>
	</ol>
	</li>
	<li>Immunoprecipitation
	<ol>
		<li>Add 20 &#956;L of Protein A beads into a 1.5 mL microcentrifuge tube.</li>
		<li>Wash the beads with 400 &#956;L of fCLIP lysis buffer. Centrifuge the beads at 1,000 x g at 4 &#176;C for 1 min. Remove the supernatant and add 400 &#956;L of fCLIP lysis buffer carefully. Gently re-suspend the beads by inverting 3~4 times.</li>
		<li>Repeat the wash step three times. After the final wash, remove the supernatant completely.</li>
		<li>Re-suspend the beads in 300 &#956;L of fCLIP lysis buffer. Add 8.3 &#956;L of 5 M NaCl to adjust NaCl concentration to ~150 mM. Add 10 &#956;L of PKR antibody and incubate for 3 h on a rotator at 4 &#176;C.</li>
		<li>Centrifuge the beads at 1,000 x g at 4 &#176;C for 1 min. Remove the supernatant and add 400 &#956;L of fCLIP wash buffer. Gently re-suspend the beads by inverting 3~4 times.</li>
		<li>Repeat the wash step two times. After the final wash, remove the supernatant completely. 
		NOTE: Never use a vortex mixer. Invert the tube gently with hands.</li>
		<li>Add 300 &#956;L of lysate and incubate for 3 h at 4 &#176;C on a rotator. 
		NOTE: Longer incubation time may result in increased background binding.</li>
		<li>Centrifuge the beads at 1,000 x g at 4 &#176;C for 1 min. Remove the supernatant and add 400 &#956;L of fCLIP wash buffer. Gently re-suspend the beads by inverting 3~4 times.</li>
		<li>Repeat the wash step three times. After the final wash, remove the supernatant completely.</li>
		<li>Add 300 &#956;L of fCLIP elution buffer. Incubate in a thermomixer for 3 h at 25 &#176;C to elute PKR from the beads. 
		NOTE: Prepare the fCLIP elution buffer fresh.</li>
		<li>Centrifuge at 1,000 x g at room temperature and transfer the supernatant to a clean siliconized tube. 
		NOTE: A microcentrifuge tube is also ok, but siliconized tube is preferred to prevent evaporation during the de-crosslinking step (step 2.3.12).</li>
		<li>Add 300 &#956;L of proteinase K (20 mg/mL) and incubate overnight at 65 &#176;C. 
		NOTE: Use a thermomixer with heated cover to avoid evaporation.</li>
	</ol>
	</li>
	<li>RNA extraction
	<ol>
		<li>Add 580 &#956;L of acid-phenol chloroform and vortex for 30 s. Incubate at 37 &#176;C for 1 h.</li>
		<li>Vortex for 30 s and centrifuge at 12,000 x g at room temperature for 10 min.</li>
		<li>Transfer the top layer into a clean 1.5 mL microcentrifuge tube. Add 1/10 volume of 3 M NaOAc, 0.5 &#956;L of coprecipitant (e.g., Glycoblue), and an equal volume of isopropanol. Incubate overnight at -20 &#176;C.</li>
		<li>Precipitate pellets by centrifuging at maximum speed at 4 &#176;C for 1 h. 
		NOTE: If RNA/DNA pellets were not observed, add an additional 0.5 &#956;L of coprecipitant and centrifuge for an additional 1 h. Continue this step until RNA/DNA pellets are observed.</li>
		<li>Remove the supernatant and add 1 mL of 75% ethyl alcohol. Centrifuge at 12,000 x g at 4 &#176;C for 5 min. Repeat the wash step one more time. Remove the supernatant completely and dry the pellet at room temperature.</li>
		<li>Add 42 &#956;L of TDW, 5 &#956;L of DNase I buffer, 1 &#956;L of RNase Inhibitor, and 2 &#956;L of DNase I. Incubate at 37 &#176;C for 1 h.</li>
		<li>Add 150 &#956;L of TDW and 200 &#956;L of acid-phenol chloroform. Vortex for 30 s. Centrifuge at 12,000 x g at room temperature for 10 min.</li>
		<li>Transfer the top layer into a clean 1.5 mL microcentrifuge tube. Add 20 &#956;L of 3 M NaOAc, 0.5 &#956;L of coprecipitant, and 1 mL of 100% ethyl alcohol. Incubate overnight at -80 &#176;C.</li>
		<li>Precipitate pellets and wash with 75% ethyl alcohol as described in steps 2.4.4 to 2.4.5.</li>
		<li>Re-suspend in the appropriate amount of TDW.</li>
	</ol>
	</li>
</ol>
3. Sequencing Library Preparation
<ol>
	<li>rRNA removal
	<ol>
		<li>Re-suspend the RNA pellets from step 2.4.10 with 28 &#956;L of TDW. 
		NOTE: The maximum amount of total RNA should be less than 5 &#956;g.</li>
		<li>Follow the procedures provided by the rRNA removal kit&#8217;s reference guide to remove rRNA.</li>
		<li>Clean up rRNA depleted RNAs by adding 160 &#956;L of magnetic beads.
		<ol>
			<li>Mix by pipetting ~15 times and incubate at room temperature for 15 min.</li>
			<li>Attach the tube on a magnetic bar and remove the supernatant.</li>
			<li>Add 300 &#956;L of 80% ethyl alcohol while the beads are still attached on the magnetic bar and incubate for 30 s.</li>
			<li>Replace ethyl alcohol with a fresh 300 &#956;L solution. Air dry the beads on the magnetic bar for 12 min at room temperature.</li>
			<li>Re-suspend the beads in 12 &#956;L of TDW and mix by pipetting 15 times.</li>
			<li>Attach the beads on the magnetic bar and move the supernatant to a clean PCR tube.</li>
		</ol>
		</li>
		<li>Deplete the fragmented ribosomal RNAs (rRNAs) following the procedures provided by rRNA Depletion Kit.</li>
		<li>Clean up the RNAs by adding 110 &#956;L of magnetic beads and repeating steps 3.1.3.1 to 3.1.3.6.</li>
	</ol>
	</li>
	<li>RNA labeling and adaptor ligation
	<ol>
		<li>On rRNA-depleted RNAs, add 2 &#956;L of 10x CIAP buffer, 1 &#956;L of RNase inhibitor, and 2 &#956;L of antarctic alkaline phosphatase. Incubate at 37 &#176;C for 1 h and then at 65 &#176;C for 5 min to inactivate the phosphatase.</li>
		<li>Add 3 &#956;L of 10x PNK buffer, 1.5 &#956;L of RNase inhibitor, 1.5 &#956;L of T4 PNK enzyme, 0.8 &#956;L of r-ATP, and 1.7 &#956;L of TDW. Incubate at 37 &#176;C for 50 min.</li>
		<li>Add 1.5 &#956;L of 10 mM ATP and incubate at 37 &#176;C for additional 40 min.</li>
		<li>Stop the reaction by adding 170 &#956;L of the RNA elution buffer.</li>
		<li>Add 200 &#956;L of acid-phenol chloroform and vortex for 30 s. Centrifuge at 12,000 x g at room temperature for 10 min.</li>
		<li>Transfer the top layer into a clean 1.5 mL microcentrifuge tube. Add 20 &#956;L of 3 M NaOAc, 0.5 &#956;L of coprecipitant, and 1 mL of 100% ethyl alcohol. Incubate overnight at -80 &#176;C.</li>
		<li>Precipitate RNA pellets and wash with 75% ethyl alcohol as described in steps 2.4.4 to 2.4.5. Re-suspend in 4.5 &#956;L of TDW and add 9 &#956;L of 2x RNA loading dye.</li>
		<li>Heat the sample at 95 &#176;C for 5 min and load on a 10% Urea-PAGE gel.</li>
		<li>Run the gel at 370 V for 40 min. 
		NOTE: Pre-run the gel at 370 V for 90 min before loading the sample.</li>
		<li>Cut the gel at the ~100 &#8211; 500 nucleotide region and break the gel.</li>
		<li>Add 700 &#956;L of 0.3 M NaCl and incubate overnight at 4 &#176;C on a rotator.</li>
		<li>Transfer the solution to a column and centrifuge at maximum speed at room temperature for 5 min.</li>
		<li>Transfer the eluate into a clean 1.5 mL microcentrifuge tube. Add 1/10 volume of 3 M NaOAc, 0.5 &#956;L of coprecipitant, and an equal volume of isopropanol. Incubate overnight at -20 &#176;C.</li>
	</ol>
	</li>
	<li>3&#39; adaptor ligation
	<ol>
		<li>Precipitate RNA pellets and wash with 75% ethyl alcohol as described in steps 2.4.4 to 2.4.5.</li>
		<li>Re-suspend the RNA pellets in 6.5 &#956;L of TDW and add 1 &#956;L of 10 &#956;M 3&#39; adaptor.</li>
		<li>Transfer the solution to a PCR tube and incubate at 70 &#176;C for 2 min.</li>
		<li>Add 1 &#956;L of 10x ligation buffer, 0.5 &#956;L of RNase inhibitor, and 1 &#956;L of T4 RNA ligase 2. Incubate at 28 &#176;C for 1 h, 25 &#176;C for 6 h, and 22 &#176;C for 6 h.</li>
		<li>Add 12 &#956;L of 2x RNA loading dye and heat at 95 &#176;C for 5 min.</li>
		<li>Gel purify the 3&#39; adaptor ligated RNAs as described in 3.2.9 to 3.2.13.</li>
	</ol>
	</li>
	<li>5&#39; adaptor ligation
	<ol>
		<li>Precipitate RNA pellets and wash with 75% ethyl alcohol as described in steps 2.4.4 to 2.4.5.</li>
		<li>Re-suspend the RNA pellets in 4.2 &#956;L of TDW and add 1 &#956;L of 5 &#956;M 5&#39; adaptor.</li>
		<li>Transfer the solution to a PCR tube and incubate at 70 &#176;C for 2 min.</li>
		<li>Add 0.8 &#956;L of 10x ligase buffer, 0.4 &#956;L of RNase inhibitor, 0.8 &#956;L of 10 mM ATP, 0.8 &#956;L of T4 RNA ligase 1. Incubate at 28 &#176;C for 1 h, 25 &#176;C for 6 h, and 22 &#176;C for 6 h.</li>
	</ol>
	</li>
	<li>Reverse transcription and PCR amplification
	<ol>
		<li>On 5&#8217; adaptor ligated RNAs, add 1 &#956;L of 4 &#956;M reverse transcription primer. Incubate at 70 &#176;C for 2 min and immediately cool to 4 &#176;C.</li>
		<li>Add 4 &#956;L of 5x FS buffer, 4 &#956;L of 2.5 mM dNTP, 1 &#956;L of 0.1 M DTT, 1 &#956;L of RNase inhibitor, and 1 &#956;L of reverse transcriptase. Incubate at 50 &#176;C for 1 h and 70 &#176;C for 15 min.</li>
		<li>Prepare PCR amplification
		<ol>
			<li>Mix 1 &#956;L of RT product, 1 &#956;L of 25 &#956;M RPI primer, 1 &#956;L of 25 &#956;M RP1 primer, 10 &#956;L of 5x HF buffer, 4 &#956;L of 2.5 mM dNTP, 32.5 &#956;L of TDW, and 0.5 &#956;L of high-fidelity polymerase.</li>
			<li>Run PCR program for 11~13 cycles. 
			NOTE: The program for the PCR is: 98 &#176;C for 30 s for a hot start, 98 &#176;C for 10 s, 60 &#176;C for 30 s and 72 &#176;C for 45 s for amplification, and 72 &#176;C for 5 min. The amplification step is repeated for 11-13 cycles.</li>
		</ol>
		</li>
		<li>Clean up the PCR products using 40 &#956;L of the magnetic beads and following steps 3.1.3.1 to 3.1.3.6 but using 10 &#956;L of TDW to elute the DNA.</li>
		<li>Add 2 &#956;L of 10x DNA loading dye. Load the sample on a 6% acrylamide gel and run at 200 V for 30 min.</li>
		<li>Stain with Sybr gold (0.01% (v/v) in 1x TBE buffer) for 5 min at room temperature.</li>
		<li>De-stain in 1x TBE buffer for 5 min at room temperature.</li>
		<li>Cut the gel at the ~200 &#8211; 700 nucleotide region and break the gel.</li>
		<li>Add 700 &#956;L of 0.3 M NaCl and incubate overnight at room temperature to elute the DNA.</li>
		<li>Load everything onto a column and centrifuge at maximum speed at room temperature for 5 min.</li>
		<li>Transfer the eluate into a clean 1.5 mL microcentrifuge tube. Add 1/10 volume of 3 M NaOAc, 0.5 &#956;L of coprecipitant, and an equal volume of isopropanol. Incubate overnight at -20 &#176;C.</li>
		<li>Precipitate DNA pellets and wash with 75% ethyl alcohol as described in steps 2.4.4 to 2.4.5. Re-suspend in 20 &#956;L of TDW.</li>
		<li>Analyze the sample using a sequencer.</li>
	</ol>
	</li>
</ol>
4. Analysis of PKR-interacting RNAs using qRT-PCR
<ol>
	<li>Method 1: Random hexamer reverse transcription
	<ol>
		<li>Re-suspend RNA pellets from step 2.4.10 with 8.5 &#956;L of TDW and transfer the solution to a PCR tube.</li>
		<li>Add 0.5 &#956;L of 100 &#956;M random hexamers and 4 &#956;L of 2.5 mM dNTP mix.</li>
		<li>Heat the solution at 65 &#176;C for 5 min and immediately incubate on ice for at least 1 min.</li>
		<li>Make the reaction mix: 4 &#956;L of 5x SSIV buffer, 1 &#956;L of 100 mM DTT, 1 &#956;L of RNase Inhibitor, and 1 &#956;L of reverse transcriptase (200 U/&#956;L). Add the reaction mix to the RNA solution.</li>
		<li>Incubate the mixture at 23 &#176;C for 10 min, 50 &#176;C for 10 min, and 80 &#176;C for 10 min.</li>
		<li>Analyze the cDNA using a real-time PCR system. 
		NOTE: The program for the real-time PCR is: 95 &#176;C for 3 min for hot start, 95 &#176;C for 5 s and 60 &#176;C for 10 s for amplification, and 95 &#176;C for 30 s, 65 &#176;C for 30 s, and 95 &#176;C for 30 s for melt. The amplification step is repeated for 40 cycles.</li>
	</ol>
	</li>
	<li>Method 2: Strand-specific reverse transcription
	<ol>
		<li>Prepare a master mix of reverse primers: Mix equal amounts of gene specific reverse transcription primers containing CMV promoter sequence followed by ~20 nucleotides of gene specific sequences. 
		NOTE: The combined concentration of all gene specific RT primers is 4 &#956;M.</li>
		<li>Re-suspend RNA pellets from step 2.4.10 with 8.5 &#956;L of TDW and transfer the solution to a PCR tube.</li>
		<li>Add 0.5 &#956;L of 4 &#956;M master mix of reverse transcription primers and 4 &#956;L of 2.5 mM dNTP mix.</li>
		<li>Heat the solution at 65 &#176;C for 5 min and immediately incubate on ice for at least 1 min.</li>
		<li>Prepare the reaction solution by mixing 4 &#956;L of 5x SSIV buffer, 1 &#956;L of 100 mM DTT, 1 &#956;L of RNase Inhibitor, and 1 &#956;L of reverse transcriptase (200 U/&#956;L). Add the reaction solution to the RNA-primer mix.</li>
		<li>Incubate the solution at 50 &#176;C for 10 min and 80 &#176;C for 10 min.</li>
		<li>Analyze the cDNA using the real-time PCR system. 
		NOTE: The program for the real-time PCR is same as the one described in Method 1.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Meurs, E. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Constitutive+expression+of+human+double-stranded+RNA-activated+p68+kinase+in+murine+cells+mediates+phosphorylation+of+eukaryotic+initiation+factor+2+and+partial+resistance+to+encephalomyocarditis+virus+growth.">Constitutive expression of human double-stranded RNA-activated p68 kinase in murine cells mediates phosphorylation of eukaryotic initiation factor 2 and partial resistance to encephalomyocarditis virus growth.</a> Journal of Virology. 66 (10), 5805-5814 (1992).</li><li>Patel, R. C., Stanton, P., McMillan, N. M., Williams, B. R., Sen, G. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+interferon-inducible+double-stranded+RNA-activated+protein+kinase+self-associates+in+vitro+and+in+vivo.">The interferon-inducible double-stranded RNA-activated protein kinase self-associates in vitro and in vivo.</a> Proceedings of the National Academy of Sciences. 92 (18), 8283-8287 (1995).</li><li>Bennett, R. L., Pan, Y., Christian, J., Hui, T., May, W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+RAX/PACT-PKR+stress+response+pathway+promotes+p53+sumoylation+and+activation,+leading+to+G(1)+arrest.">The RAX/PACT-PKR stress response pathway promotes p53 sumoylation and activation, leading to G(1) arrest.</a> Cell Cycle. 11 (1), 407-417 (2012).</li><li>Yang, X., Nath, A., Opperman, M. J., Chan, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+double-stranded+RNA-dependent+protein+kinase+differentially+regulates+insulin+receptor+substrates+1+and+2+in+HepG2+cells.">The double-stranded RNA-dependent protein kinase differentially regulates insulin receptor substrates 1 and 2 in HepG2 cells.</a> Molecular and Cellular Biology. 21 (19), 3449-3458 (2010).</li><li>Zamanian-Daryoush, M., Mogensen, T. H., DiDonato, J. A., Williams, B. R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NF-kappa+B+Activation+by+Double-Stranded-RNA-Activated+Protein+Kinase+(PKR)+Is+Mediated+through+NF-kappa+B-Inducing+Kinase+and+Ikappa+B+Kinase.">NF-kappa B Activation by Double-Stranded-RNA-Activated Protein Kinase (PKR) Is Mediated through NF-kappa B-Inducing Kinase and Ikappa B Kinase.</a> Molecular and Cellular Biology. 20 (4), 1278-1290 (2000).</li><li>Takada, Y., Ichikawa, H., Pataer, A., Swisher, S., Aggarwal, B. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genetic+deletion+of+PKR+abrogates+TNF-induced+activation+of+IkappaBalpha+kinase.">Genetic deletion of PKR abrogates TNF-induced activation of IkappaBalpha kinase.</a> JNK, Akt and cell proliferation but potentiates p44/p42 MAPK and p38 MAPK activation. Oncogene. 26 (8), 1201-1212 (2007).</li><li>Dabo, S., Meurs, E. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=dsRNA-dependent+protein+kinase+PKR+and+its+role+in+stress,+signaling+and+HCV+infection.">dsRNA-dependent protein kinase PKR and its role in stress, signaling and HCV infection.</a> Viruses. 4 (11), 2598-2635 (2012).</li><li>Black, T. L., Safer, B., Hovanessian, A., Katze, M. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Cellular+68,000-Mr+Protein-Kinase+Is+Highly+Autophosphorylated+and+Activated+yet+Significantly+Degraded+during+Poliovirus+Infection+-+Implications+for+Translational+Regulation.">The Cellular 68,000-Mr Protein-Kinase Is Highly Autophosphorylated and Activated yet Significantly Degraded during Poliovirus Infection - Implications for Translational Regulation.</a> Journal of Virology. 63 (5), 2244-2251 (1989).</li><li>Bando, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Double-strand+RNA+dependent+protein+kinase+(PKR)+is+involved+in+the+extrastriatal+degeneration+in+Parkinson's+disease+and+Huntington's+disease.">Double-strand RNA dependent protein kinase (PKR) is involved in the extrastriatal degeneration in Parkinson's disease and Huntington's disease.</a> Neurochemistry International. 46 (1), 11-18 (2005).</li><li>Onuki, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+RNA-dependent+protein+kinase+is+involved+in+tunicamycin-induced+apoptosis+and+Alzheimer's+disease.">An RNA-dependent protein kinase is involved in tunicamycin-induced apoptosis and Alzheimer's disease.</a> The EMBO Journal. 23 (4), 959-968 (2004).</li><li>Peel, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+the+cell+stress+kinase+PKR+in+Alzheimer's+disease+and+human+amyloid+precursor+protein+transgenic+mice.">Activation of the cell stress kinase PKR in Alzheimer's disease and human amyloid precursor protein transgenic mice.</a> Neurobiology of Disease. 14 (1), 52-62 (2003).</li><li>Peel, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Double-stranded+RNA-dependent+protein+kinase,+PKR,+binds+preferentially+to+Huntington's+disease+(HD)+transcripts+and+is+activated+in+HD+tissue.">Double-stranded RNA-dependent protein kinase, PKR, binds preferentially to Huntington's disease (HD) transcripts and is activated in HD tissue.</a> Human Molecular Genetics. 10 (15), 1531-1538 (2001).</li><li>Suen, K. C., Yu, M. S., So, K. F., Chang, R. C., Hugon, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Upstream+signaling+pathways+leading+to+the+activation+of+double-stranded+RNA-dependent+serine/threonine+protein+kinase+in+beta-amyloid+peptide+neurotoxicity.">Upstream signaling pathways leading to the activation of double-stranded RNA-dependent serine/threonine protein kinase in beta-amyloid peptide neurotoxicity.</a> Journal of biological chemistry. 278 (50), 49819-49827 (2003).</li><li>Nakamura, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+critical+role+for+PKR+complexes+with+TRBP+in+Immunometabolic+regulation+and+eIF2alpha+phosphorylation+in+obesity.">A critical role for PKR complexes with TRBP in Immunometabolic regulation and eIF2alpha phosphorylation in obesity.</a> Cell Reports. 11 (2), 295-307 (2015).</li><li>Saito, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhancement+of+the+interferon-induced+double-stranded+RNA-dependent+protein+kinase+activity+by+Sindbis+virus+infection+and+heat-shock+stress.">Enhancement of the interferon-induced double-stranded RNA-dependent protein kinase activity by Sindbis virus infection and heat-shock stress.</a> Microbiology and Immunology. 34 (10), 859-870 (1990).</li><li>Youssef, O. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Potential+role+for+snoRNAs+in+PKR+activation+during+metabolic+stress.">Potential role for snoRNAs in PKR activation during metabolic stress.</a> Proceedings of the National Academy of Sciences. 112 (16), 5023-5028 (2015).</li><li>Murtha-Riel, P., Davies, M. V., Choi, S. Y., Hershey, J. W., Kaufman, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+of+a+Phosphorylation-resistant+Eukaryotic+Initiation+Factor+2+a-Subunit+Mitigates+Heat+Shock+Inhibition+of+Protein+Synthesis.">Expression of a Phosphorylation-resistant Eukaryotic Initiation Factor 2 a-Subunit Mitigates Heat Shock Inhibition of Protein Synthesis.</a> The Journal of Biological Chemistry. 268, 12946-12951 (1993).</li><li>Benkirane, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oncogenic+potential+of+TAR+RNA+binding+protein+TRBP+and+its+regulatory+interaction+with+RNA-dependent+protein+kinase+PKR.">Oncogenic potential of TAR RNA binding protein TRBP and its regulatory interaction with RNA-dependent protein kinase PKR.</a> The EMBO Journal. 16 (3), 611-624 (1997).</li><li>Koromilas, A., Roy, S., Barber, G., Katze, M., Sonenberg, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Malignant+transformation+by+a+mutant+of+the+IFN-inducible+dsRNA-dependent+protein+kinase.">Malignant transformation by a mutant of the IFN-inducible dsRNA-dependent protein kinase.</a> Science. 257 (5077), 1685-1689 (1992).</li><li>Kim, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PKR+is+activated+by+cellular+dsRNAs+during+mitosis+and+acts+as+a+mitotic+regulator.">PKR is activated by cellular dsRNAs during mitosis and acts as a mitotic regulator.</a> Genes &amp; Development. 28 (12), 1310-1322 (2014).</li><li>Kim, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deletion+of+human+tarbp2+reveals+cellular+microRNA+targets+and+cell-cycle+function+of+TRBP.">Deletion of human tarbp2 reveals cellular microRNA targets and cell-cycle function of TRBP.</a> Cell Reports. 9 (3), 1061-1074 (2014).</li><li>Zhu, P. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Suppression+of+PKR+promotes+network+excitability+and+enhanced+cognition+by+interferon-gamma-mediated+disinhibition.">Suppression of PKR promotes network excitability and enhanced cognition by interferon-gamma-mediated disinhibition.</a> Cell. 147 (6), 1384-1396 (2011).</li><li>Dagon, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Double-stranded+RNA-dependent+protein+kinase,+PKR,+down-regulates+CDC2/cyclin+B1+and+induces+apoptosis+in+non-transformed+but+not+in+v-mos+transformed+cells.">Double-stranded RNA-dependent protein kinase, PKR, down-regulates CDC2/cyclin B1 and induces apoptosis in non-transformed but not in v-mos transformed cells.</a> Oncogene. 20 (56), 8045-8056 (2001).</li><li>Elbarbary, R. A., Li, W., Tian, B., Maquat, L. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=STAU1+binding+3'+UTR+IRAlus+complements+nuclear+retention+to+protect+cells+from+PKR-mediated+translational+shutdown.">STAU1 binding 3' UTR IRAlus complements nuclear retention to protect cells from PKR-mediated translational shutdown.</a> Genes &amp; Development. 27 (13), 1495-1510 (2013).</li><li>Cho, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=LIN28A+is+a+suppressor+of+ER-associated+translation+in+embryonic+stem+cells.">LIN28A is a suppressor of ER-associated translation in embryonic stem cells.</a> Cell. 151 (4), 765-777 (2012).</li><li>Licatalosi, D. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HITS-CLIP+yields+genome-wide+insights+into+brain+alternative+RNA+processing.">HITS-CLIP yields genome-wide insights into brain alternative RNA processing.</a> Nature. 456 (7221), 464-469 (2008).</li><li>Van Nostrand, E. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Robust+transcriptome-wide+discovery+of+RNA-binding+protein+binding+sites+with+enhanced+CLIP+(eCLIP).">Robust transcriptome-wide discovery of RNA-binding protein binding sites with enhanced CLIP (eCLIP).</a> Nature Methods. 13 (6), 508-514 (2016).</li><li>Kim, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PKR+Senses+Nuclear+and+Mitochondrial+Signals+by+Interacting+with+Endogenous+Double-Stranded+RNAs.">PKR Senses Nuclear and Mitochondrial Signals by Interacting with Endogenous Double-Stranded RNAs.</a> Molecular Cell. 71 (6), 1051-1063 (2018).</li><li>Kim, B., Jeong, K., Kim, V. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genome-wide+Mapping+of+DROSHA+Cleavage+Sites+on+Primary+MicroRNAs+and+Noncanonical+Substrates.">Genome-wide Mapping of DROSHA Cleavage Sites on Primary MicroRNAs and Noncanonical Substrates.</a> Molecular Cell. 66 (2), 258-269 (2017).</li><li>Ricci, E. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Staufen1+senses+overall+transcript+secondary+structure+to+regulate+translation.">Staufen1 senses overall transcript secondary structure to regulate translation.</a> Nature Structural &amp; Molecular Biology. 21 (1), 26-35 (2014).</li><li>Kim, B., Kim, V. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=fCLIP-seq+for+transcriptomic+footprinting+of+dsRNA-binding+proteins:+Lessons+from+DROSHA.">fCLIP-seq for transcriptomic footprinting of dsRNA-binding proteins: Lessons from DROSHA.</a> Methods. , (2018).</li><li>Dhir, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitochondrial+double-stranded+RNA+triggers+antiviral+signalling+in+humans.">Mitochondrial double-stranded RNA triggers antiviral signalling in humans.</a> Nature. 560 (7717), 238-242 (2018).</li></ol>

The authors have nothing to disclose.

The process to prepare S or M phase-arrested samples is illustrated in Figure 1. To arrest cells at the S phase, we used a thymidine double block method where we treated cells with thymidine two times with a 9 h release in between to ensure high arrest efficiency (Figure 1A). For M phase arrest, we treated cells once with thymidine followed by a 9 h release and then applied nocodazole to block cells at prometaphase (Figure 1B). One ...

Protein kinase RNA-activated (PKR), also known as eukaryotic initiation factor 2-alpha kinase 2 (EIF2AK2), is a well-characterized protein kinase that transmits information provided by RNAs. It belongs to the eukaryotic translation initiation 2 subunit alpha (eIF2&#945;) kinase family and phosphorylates eIF2&#945; at serine 51 in response to infection to suppress global translation1. In this context, PKR is activated by viral double-stranded RNAs (dsRNAs), which provide a platform for PKR dimerization and autophosphorylation2. In addition to eIF2&#945;, PKR can also phosphorylate p53, insulin receptor substrate 1, inhibitor &#954;B, and c-Jun N-terminal kinase (JNK) to regulate activity of numerous signal transduction pathways3,4,5,6.
PKR was originally identified as a kinase that phosphorylated eIF2&#945; during poliovirus infection by recognizing poliovirus&#8217; dsRNAs7,8. PKR is increasingly found to play multifaceted roles beyond immune response, and its aberrant activation or malfunction is implied in numerous human diseases. Activated/Phosphorylated PKR (pPKR) is frequently observed during apoptosis and is a common characteristic of patients with degenerative diseases, particularly neurodegenerative diseases such as Huntington&#8217;s, Parkinson&#8217;s, and Alzheimer&#8217;s disease9,10,11,12,13. In addition, PKR is activated under various stress conditions such as metabolic stress and heat shock14,15,16,17. On the other hand, inhibition of PKR results in increased cell proliferation and even malignant transformation18,19. PKR function is also important in normal brain function and during the cell cycle as the level of pPKR is elevated during the M phase20,21,22. In this context, pPKR suppresses global translation and provides cues to key mitotic signaling systems that are required for proper cell division20. Moreover, prolonged activation of PKR resulted in G2/M phase cell cycle arrest in Chinese hamster ovary cells23. Consequently, PKR phosphorylation is regulated by the negative feedback loop to ensure rapid deactivation during M/G1 transition21.
Despite the wide range of PKR function, our understanding of PKR activation is limited due to the lack of a standardized high-throughput experimental approach to capture and identify dsRNAs that can activate PKR. Previous studies have shown that PKR can interact with dsRNAs formed by two inverted Alu repeats (IRAlus)20,24, but the possibility of the existence of additional cellular dsRNAs that can activate PKR during the cell cycle or under stress conditions in human cells was unexplored. The conventional approach in identifying RNA-interactors of an RNA binding protein (RBP) uses UV light to crosslink RNA-RBP complexes25,26,27. A recent study applied this UV crosslinking approach in a mouse system and identified that small nucleolar RNAs can regulate PKR activation during metabolic stress16. By utilizing high crosslinking efficiency of formaldehyde, &#160;we presented an alternative method to identify PKR-interacting RNAs during the cell cycle in HeLa cells28. A similar approach has been applied to study other dsRBPs such as Staufen and Drosha29,30,31. We found that PKR can interact with various types of noncoding RNAs such as short interspersed nuclear element (SINE), long interspersed nuclear element (LINE), endogenous retrovirus element (ERV), and even alpha-satellite RNAs. In addition, we showed that PKR can interact with mitochondrial RNAs (mtRNAs), which form intermolecular dsRNAs through complementary interaction between the heavy-strand and the light strand RNAs28. A recent publication further supported our data that some mtRNAs exist in a duplex form and can activate dsRNA sensors such as melanoma differentiation-associated protein 5 to induce interferons32. More importantly, the expression and subcellular localization of mtRNAs are modulated during the cell cycle and by various stressors, which may be important in their ability to regulate PKR activation28.
In this article, we present a detailed protocol for a recently developed formaldehyde crosslinking and immunoprecipitation (fCLIP) method to capture and analyze PKR-interacting RNAs during the cell cycle. We demonstrate the method to prepare cell cycle arrest samples using thymidine and nocodazole. We then present the fCLIP process to isolate PKR-bound RNAs and a method to prepare high-throughput sequencing library to identify these RNAs. Furthermore, we delineate detailed procedures to analyze PKR-bound RNAs using qRT-PCR. Specifically, we present a strand-specific reverse transcription procedure to analyze the strandedness of mtRNAs. The described protocol is optimized for HeLa cells and PKR, but key steps such as the preparation of cell cycle sample, fCLIP, and strand-specific qRT-PCR analysis can be easily modified to study cellular dsRNAs or to identify RNA interactors of other dsRBPs.

<table>
	<tbody>
		<tr>
			<td>0.5 M EDTA, pH 8.0</td>
			<td>Thermo Fisher Scientific</td>
			<td>AM9260G</td>
			<td></td>
		</tr>
		<tr>
			<td>1 M Tris, pH 7.0</td>
			<td>Thermo Fisher Scientific</td>
			<td>AM9855G</td>
			<td></td>
		</tr>
		<tr>
			<td>1 M Tris, pH 8.0</td>
			<td>Thermo Fisher Scientific</td>
			<td>AM9855G</td>
			<td></td>
		</tr>
		<tr>
			<td>1.7 mL microcentrifuge tube</td>
			<td>Axygen</td>
			<td>MCT-175-C</td>
			<td></td>
		</tr>
		<tr>
			<td>10% Nonidet-p40 (NP-40)</td>
			<td>Biosolution</td>
			<td>BN015</td>
			<td></td>
		</tr>
		<tr>
			<td>10% Urea-acrylamide gel solution</td>
			<td></td>
			<td></td>
			<td>7 M (w/v) Urea and 0.5X TBE, stored protected from light at 4 &#176;C</td>
		</tr>
		<tr>
			<td>10X DNA loading buffer</td>
			<td>TaKaRa</td>
			<td>9157</td>
			<td></td>
		</tr>
		<tr>
			<td>15 mL conical tube</td>
			<td>SPL</td>
			<td>50015</td>
			<td></td>
		</tr>
		<tr>
			<td>3&#39; adaptor</td>
			<td></td>
			<td></td>
			<td>5&#39;-rApp NN NNT GGA ATT CTC GGG TGC CAA GG/3ddC/-3&#39;</td>
		</tr>
		<tr>
			<td>3 M Sodium Acetate pH 5.5</td>
			<td>Thermo Fisher Scientific</td>
			<td>AM9740</td>
			<td></td>
		</tr>
		<tr>
			<td>5&#39; adaptor</td>
			<td></td>
			<td></td>
			<td>5&#39;-GUU CAG AGU UCU ACA GUC CGA CGA UCN NNN-3&#39;</td>
		</tr>
		<tr>
			<td>5 M NaCl</td>
			<td>Thermo Fisher Scientific</td>
			<td>AM9760G</td>
			<td></td>
		</tr>
		<tr>
			<td>50 mL conical tube</td>
			<td>SPL</td>
			<td>50050</td>
			<td></td>
		</tr>
		<tr>
			<td>Acid-phenol chloroform, pH 4.5</td>
			<td>Thermo Fisher Scientific</td>
			<td>AM9722</td>
			<td></td>
		</tr>
		<tr>
			<td>Agencourt AMPure XP</td>
			<td>Beckman Coulter</td>
			<td>A63881</td>
			<td>Magnetic beads DNA/RNA clean up</td>
		</tr>
		<tr>
			<td>Antarctic alkaline phosphatase</td>
			<td>New England Biolabs</td>
			<td>M0289S</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-DGCR8</td>
			<td></td>
			<td></td>
			<td>Made in house</td>
		</tr>
		<tr>
			<td>Anti-PKR (D7F7)</td>
			<td>Cell signaling technology</td>
			<td>12297S</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-PKR (Milli)</td>
			<td>Millipore EMD</td>
			<td>07-151</td>
			<td></td>
		</tr>
		<tr>
			<td>ATP (100 mM)</td>
			<td>GE Healthcare</td>
			<td>GE27-2056-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Bromophenol blue sodium salt</td>
			<td>Sigma-aldrich</td>
			<td>B5525</td>
			<td></td>
		</tr>
		<tr>
			<td>Calf intestinal alkaline phosphatase</td>
			<td>TaKaRa</td>
			<td>2250A</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell scraper 25 cm 2-position</td>
			<td>Sarstedt</td>
			<td>83.183</td>
			<td></td>
		</tr>
		<tr>
			<td>CMV promoter sequence</td>
			<td></td>
			<td></td>
			<td>5&#39;-CGCAAATGGGCGGTAGGCGTG-3&#39;</td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s modified eagle medium</td>
			<td>Welgene</td>
			<td>LM001-05</td>
			<td></td>
		</tr>
		<tr>
			<td>dNTP mixture (2.5 mM)</td>
			<td>TaKaRa</td>
			<td>4030</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol, Absolute, ACS Grade</td>
			<td>Alfa-Aesar</td>
			<td>A9951</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum</td>
			<td>Merck</td>
			<td>M-TMS-013-BKR</td>
			<td></td>
		</tr>
		<tr>
			<td>Formamide</td>
			<td>Merck</td>
			<td>104008</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycine</td>
			<td>Bio-basic</td>
			<td>GB0235</td>
			<td></td>
		</tr>
		<tr>
			<td>GlycoBlue coprecipitant (15 mg/mL)</td>
			<td>Thermo Fisher Scientific</td>
			<td>AM9516</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>Merck</td>
			<td>8.18766.1000</td>
			<td></td>
		</tr>
		<tr>
			<td>NEBNext rRNA Depletion Kit</td>
			<td>New England Biolabs</td>
			<td>E6318</td>
			<td>rRNA Depletion Kit</td>
		</tr>
		<tr>
			<td>Nocodazole</td>
			<td>Sigma-Aldrich</td>
			<td>M1404</td>
			<td></td>
		</tr>
		<tr>
			<td>Normal rabbit IgG</td>
			<td>Cell signaling technology</td>
			<td>2729S</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma-Aldrich</td>
			<td>6148</td>
			<td></td>
		</tr>
		<tr>
			<td>PCR forward primer (RP1)</td>
			<td></td>
			<td></td>
			<td>5&#39;-AAT GAT ACG GCG ACC ACC GCG ATC TAC ACG TTC AGA GTT CTA CAG TCC GA-3&#39;</td>
		</tr>
		<tr>
			<td>PCR index reverse primer (RPI)</td>
			<td></td>
			<td></td>
			<td>5&#39;-CAA GCA GAA GAC GGC ATA CGA GAT NNN NNN GTG ACT GGA GTT CCT TGG CAC CCG AGA ATT CCA-3&#39;</td>
		</tr>
		<tr>
			<td>PCR tubes with flat cap, 0.2 mL</td>
			<td>Axygen</td>
			<td>PCR-02-C</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate bufered saline (PBS) Tablet</td>
			<td>TaKaRa</td>
			<td>T9181</td>
			<td></td>
		</tr>
		<tr>
			<td>Phusion high-fidelity DNA polymerase</td>
			<td>New England Biolabs</td>
			<td>M0530</td>
			<td>High-fidelity polymerase</td>
		</tr>
		<tr>
			<td>PlateFuge microcentrifuge with swing-out rotor</td>
			<td>Benchmark</td>
			<td>c2000</td>
			<td></td>
		</tr>
		<tr>
			<td>Polynucleotide kinase (PNK)</td>
			<td>TaKaRa</td>
			<td>2021A</td>
			<td></td>
		</tr>
		<tr>
			<td>Protease inhibitor cocktail set III</td>
			<td>Merck</td>
			<td>535140-1MLCN</td>
			<td></td>
		</tr>
		<tr>
			<td>Proteinase K, recombinant, PCR Grade</td>
			<td>Sigma-Aldrich</td>
			<td>3115879001</td>
			<td></td>
		</tr>
		<tr>
			<td>qPCR primer sequence: CO1 Heavy</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-GCCATAACCCAATACCAAACG-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: CO1 Light</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-TTGAGGTTGCGGTCTGTTAG-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: CO2 Heavy</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-CTAGTCCTGTATGCCCTTTTCC-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: CO2 Light</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-GTAAAGGATGCGTAGGGATGG-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: CO3 Heavy</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-CCTTTTACCACTCCAGCCTAG-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: CO3 Light</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-CTCCTGATGCGAGTAATACGG-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: CYTB Heavy</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-CAATTATACCCTAGCCAACCCC-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: CYTB Light</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-GGATAGTAATAGGGCAAGGACG -3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: GAPDH</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-CAACGACCACTTTGTCAAGC-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: ND1 Heavy</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-TCAAACTCAAACTACGCCCTG-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: ND1 Light</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-GTTGTGATAAGGGTGGAGAGG-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: ND4 Heavy</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-CTCACACTCATTCTCAACCCC-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: ND4 Light</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-TGTTTGTCGTAGGCAGATGG-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: ND5 Heavy</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-CTAGGCCTTCTTACGAGCC-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: ND5 Light</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-TAGGGAGAGCTGGGTTGTTT-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: ND6 Heavy</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-TCATACTCTTTCACCCACAGC-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>qPCR primer sequence: ND6 Light</td>
			<td></td>
			<td></td>
			<td>Forward/Reverse: 5&#8242;-TGCTGTGGGTGAAAGAGTATG-3&#8242;/5&#8242;-CGCAAATGGGCGGTAGGCGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>Random hexamer</td>
			<td>Thermo Fisher Scientific</td>
			<td>SO142</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant Dnase I (Rnase-free) (5 U/&#956;L)</td>
			<td>TaKaRa</td>
			<td>2270A</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant Rnase inhibitor (40 U/&#956;L)</td>
			<td>TaKaRa</td>
			<td>2313A</td>
			<td></td>
		</tr>
		<tr>
			<td>Ribo-Zero rRNA Removal Kit</td>
			<td>Illumina</td>
			<td>MRZH116</td>
			<td>rRNA Removal Kit</td>
		</tr>
		<tr>
			<td>Rotator</td>
			<td>FINEPCR, ROTATOR AG</td>
			<td>D1.5-32</td>
			<td></td>
		</tr>
		<tr>
			<td>RT primer sequence: CO1 Heavy</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGTTGAGGTTGCGGTCTGTTAG-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: CO1 Light</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGGCCATAACCCAATACCAAACG-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: CO2 Heavy</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGGTAAAGGATGCGTAGGGATGG-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: CO2 Light</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGCTAGTCCTGTATGCCCTTTTCC-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: CO3 Heavy</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGCTCCTGATGCGAGTAATACGG-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: CO3 Light</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGCCTTTTACCACTCCAGCCTAG-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: CYTB Heavy</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGGGATAGTAATAGGGCAAGGACG-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: CYTB Light</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGCAATTATACCCTAGCCAACCCC-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: GAPDH</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGTGAGCGATGTGGCTCGGCT-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: ND1 Heavy</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGGTTGTGATAAGGGTGGAGAGG-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: ND1 Light</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGTCAAACTCAAACTACGCCCTG-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: ND4 Heavy</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGTGTTTGTCGTAGGCAGATGG-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: ND4 Light</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGCCTCACACTCATTCTCAACCC-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: ND5 Heavy</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGTTTGGGTTGAGGTGATGATG-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: ND5 Light</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGCATTGTCGCATCCACCTTTA-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: ND6 Heavy</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGGGTTGAGGTCTTGGTGAGTG-3&#8242;</td>
		</tr>
		<tr>
			<td>RT primer sequence: ND6 Light</td>
			<td></td>
			<td></td>
			<td>5&#8242;-CGCAAATGGGCGGTAGGCGTGCCCATAATCATACAAAGCCCC-3&#8242;</td>
		</tr>
		<tr>
			<td>Siliconized polypropylene 1.5 mL G-tube</td>
			<td>Bio Plas</td>
			<td>4167SLS50</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium dedecyl sulfate</td>
			<td>Biosesang</td>
			<td>S1010</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium deoxycholate</td>
			<td>Sigma-Aldrich</td>
			<td>D6750</td>
			<td></td>
		</tr>
		<tr>
			<td>SUPERase In Rnase inhibitor</td>
			<td>Thermo Fisher Scientific</td>
			<td>AM2694</td>
			<td></td>
		</tr>
		<tr>
			<td>SuperScript III reverse transcriptase</td>
			<td>Thermo Fisher Scientific</td>
			<td>18080093</td>
			<td>Reverse transcriptase for library preparation</td>
		</tr>
		<tr>
			<td>SuperScript IV reverse transcriptase</td>
			<td>Thermo Fisher Scientific</td>
			<td>18090010</td>
			<td>Reverse transcriptase for qRT-PCR</td>
		</tr>
		<tr>
			<td>SYBR gold nucleic acid gl stain</td>
			<td>Thermo Fisher Scientific</td>
			<td>S11494</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 polynucleotide kinase</td>
			<td>New England Biolabs</td>
			<td>M0201S</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 RNA ligase 1 (ssRNA Ligase)</td>
			<td>New England Biolabs</td>
			<td>M0204</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 RNA ligase 2, truncated KQ</td>
			<td>New England Biolabs</td>
			<td>M0373</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermomixer</td>
			<td>Eppendorf ThermoMixer C with ThermoTop</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Thymidine</td>
			<td>Sigma-Aldrich</td>
			<td>T9250</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris-borate-EDTA buffer (TBE)</td>
			<td>TaKara</td>
			<td>T9122</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Promega</td>
			<td>H5142</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultralink Protein A sepharose beads</td>
			<td>Thermo Fisher Scientific</td>
			<td>22810</td>
			<td>Protein A beads</td>
		</tr>
		<tr>
			<td>Ultrasonicator</td>
			<td>Bioruptor</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Urea</td>
			<td>Bio-basic</td>
			<td>UB0148</td>
			<td></td>
		</tr>
		<tr>
			<td>Vortex mixer</td>
			<td>DAIHAN Scientific</td>
			<td>VM-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Xylene cyanol</td>
			<td>Sigma-Aldrich</td>
			<td>X4126</td>
			<td></td>
		</tr>
		<tr>
			<td>&#947;-32P-ATP (10 &#956;Ci/&#956;L, 3.3 &#956;M)</td>
			<td>PerkinElmer</td>
			<td>BLU502A100UC</td>
			<td></td>
		</tr>
	</tbody>
</table>

studying rna interactors of protein kinase rna-activated during the mammalian cell cycle

Protein kinase RNA-activated (PKR) is a member of the innate immune response proteins and recognizes the double-stranded secondary structure of viral RNAs. When bound to viral double-stranded RNAs (dsRNAs), PKR undergoes dimerization and subsequent autophosphorylation. Phosphorylated PKR (pPKR) becomes active and induces phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2&#945;) to suppress global translation. Increasing evidence suggests that PKR can be activated under physiological conditions such as during the cell cycle or under various stress conditions without infection. However, our understanding of the RNA activators of PKR is limited due to the lack of a standardized experimental method to capture and analyze PKR-interacting dsRNAs. Here, we present an experimental protocol to specifically enrich and analyze PKR bound RNAs during the cell cycle using HeLa cells. We utilize the efficient crosslinking activity of formaldehyde to fix PKR-RNA complexes and isolate them via immunoprecipitation. PKR co-immunoprecipitated RNAs can then be further processed to generate a high-throughput sequencing library. One major class of PKR-interacting cellular dsRNAs is mitochondrial RNAs (mtRNAs), which can exist as intermolecular dsRNAs through complementary interaction between the heavy-strand and the light-strand RNAs. To study the strandedness of these duplex mtRNAs, we also present a protocol for strand-specific qRT-PCR. Our protocol is optimized for the analysis of PKR-bound RNAs, but it can be easily modified to study cellular dsRNAs or RNA-interactors of other dsRNA binding proteins.

A schematic for the process to arrest HeLa cells at the S or M phase of the cell cycle is shown in Figure 1. For an M phase-arrested sample, we can clearly visualize round shaped cells under the microscope (Figure 2A). To examine the efficiency of the cell cycle arrest, the nuclear content of the cell can be analyzed using FACS (Figure 2B). Figure 3 shows representative data for immunoprecipitation efficiency test, where ...

Watch this Scientific Journal Video about Studying RNA Interactors of Protein Kinase RNA-Activated during the Mammalian Cell Cycle at JoVE.com

Studying RNA Interactors of Protein Kinase RNA-Activated during the Mammalian Cell Cycle

We present experimental approaches for studying RNA-interactors of double-stranded RNA binding protein kinase RNA-activated (PKR) during the mammalian cell cycle using HeLa cells. This method utilizes formaldehyde to crosslink RNA-PKR complexes and immunoprecipitation to enrich PKR-bound RNAs. These RNAs can be further analyzed through high-throughput sequencing or qRT-PCR.

Protein kinase RNA-activated (PKR) is a member of the innate immune response proteins and recognizes the double-stranded secondary structure of viral ...

studying-rna-interactors-protein-kinase-rna-activated-during

Research

JoVE Journal

Biochemistry

6.4K Views.  Korea Advanced Institute of Science and Technology (KAIST). We present experimental approaches for studying RNA-interactors of double-stranded RNA binding protein kinase RNA-activated (PKR) during the mammalian cell cycle using HeLa cells. This method utilizes formaldehyde to crosslink RNA-PKR complexes and immunoprecipitation to enrich PKR-bound RNAs. These RNAs can be further analyzed through high-throughput sequencing or qRT-PCR.

Video: Studying RNA Interactors of Protein Kinase RNA-Activated during the Mammalian Cell Cycle

Protein Complex Affinity Capture from Cryomilled Mammalian Cells

Affinity capture is an effective technique for isolating endogenous protein complexes for further study. When used in conjunction with an antibody, this technique is also frequently referred to as immunoprecipitation. Affinity capture can be applied in a bench-scale and in a high-throughput context. When coupled with protein mass spectrometry, affinity capture has proven to be a workhorse of interactome analysis. Although there are potentially many ways to execute the numerous steps involved, the following protocols implement our favored methods. Two features are distinctive: the use of cryomilled cell powder to produce cell extracts, and antibody-coupled paramagnetic beads as the affinity medium. In many cases, we have obtained superior results to those obtained with more conventional affinity capture practices. Cryomilling avoids numerous problems associated with other forms of cell breakage. It provides efficient breakage of the material, while avoiding denaturation issues associated with heating or foaming. It retains the native protein concentration up to the point of extraction, mitigating macromolecular dissociation. It reduces the time extracted proteins spend in solution, limiting deleterious enzymatic activities, and it may reduce the non-specific adsorption of proteins by the affinity medium. Micron-scale magnetic affinity media have become more commonplace over the last several years, increasingly replacing the traditional agarose- and Sepharose-based media. Primary benefits of magnetic media include typically lower non-specific protein adsorption; no size exclusion limit because protein complex binding occurs on the bead surface rather than within pores; and ease of manipulation and handling using magnets.

Here we describe protocols to disrupt mammalian cells by solid-state milling at a cryogenic temperature, produce a cell extract from the resulting cell powder, and isolate protein complexes of interest by affinity capture upon antibody-coupled micron-scale paramagnetic beads.

Affinity capture is an effective technique for isolating endogenous protein complexes for further study. When used in conjunction with an antibody, this ...

Time-resolved ElectroSpray Ionization Hydrogen-deuterium Exchange Mass Spectrometry for Studying Protein Structure and Dynamics

Intrinsically disordered proteins (IDPs) have long been a challenge to structural biologists due to their lack of stable secondary structure elements. Hydrogen-Deuterium Exchange (HDX) measured at rapid time scales is uniquely suited to detect structures and hydrogen bonding networks that are briefly populated, allowing for the characterization of transient conformers in native ensembles. Coupling of HDX to mass spectrometry offers several key advantages, including high sensitivity, low sample consumption and no restriction on protein size. This technique has advanced greatly in the last several decades, including the ability to monitor HDX labeling times on the millisecond time scale. In addition, by incorporating the HDX workflow onto a microfluidic platform housing an acidic protease microreactor, we are able to localize dynamic properties at the peptide level. In this study, Time-Resolved ElectroSpray Ionization Mass Spectrometry (TRESI-MS) coupled to HDX was used to provide a detailed picture of residual structure in the tau protein, as well as the conformational shifts induced upon hyperphosphorylation.

Conformational flexibility plays a critical role in protein function. Herein, we describe the use of time-resolved electrospray ionization mass spectrometry coupled to hydrogen-deuterium exchange for probing the rapid structural changes that drive function in ordered and disordered proteins.

Intrinsically disordered proteins (IDPs) have long been a challenge to structural biologists due to their lack of stable secondary structure elements. ...

Assaying Protein Kinase Activity with Radiolabeled ATP

Protein kinases are able to govern large-scale cellular changes in response to complex arrays of stimuli, and much effort has been directed at uncovering allosteric details of their regulation. Kinases comprise signaling networks whose defects are often hallmarks of multiple forms of cancer and related diseases, making an assay platform amenable to manipulation of upstream regulatory factors and validation of reaction requirements critical in the search for improved therapeutics. Here, we describe a basic kinase assay that can be easily adapted to suit specific experimental questions including but not limited to testing the effects of biochemical and pharmacological agents, genetic manipulations such as mutation and deletion, as well as cell culture conditions and treatments to probe cell signaling mechanisms. This assay utilizes radiolabeled [&#947;-32P] ATP, which allows for quantitative comparisons and clear visualization of results, and can be modified for use with immunoprecipitated or recombinant kinase, specific or typified substrates, all over a wide range of reaction conditions.

Protein kinases are highly evolved signaling enzymes and scaffolds that are critical for inter- and intracellular signal transduction. We present a protocol for measuring kinase activity through the use of radiolabeled adenosine triphosphate ([&#947;-32P] ATP), a reliable method to aid in elucidation of cellular signaling regulation.

Protein kinases are able to govern large-scale cellular changes in response to complex arrays of stimuli, and much effort has been directed at uncovering ...

Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs

Translation initiation is the rate-limiting step of protein synthesis and represents a key point at which cells regulate their protein output. Regulation of protein synthesis is the key to cellular stress-response, and dysregulation is central to many disease states, such as cancer. For instance, although cellular stress leads to the inhibition of global translation by attenuating cap-dependent initiation, certain stress-response proteins are selectively translated in a cap-independent manner. Discreet RNA regulatory elements, such as cellular internal ribosome entry sites (IRESes), allow for the translation of these specific mRNAs. Identification of such mRNAs, and the characterization of their regulatory mechanisms, have been a key area in molecular biology. Toeprinting is a method for the study of RNA structure and function as it pertains to translation initiation. The goal of toeprinting is to assess the ability of in vitro transcribed RNA to form stable complexes with ribosomes under a variety of conditions, in order to determine which sequences, structural elements, or accessory factors are involved in ribosome binding&#8212;a pre-cursor for efficient translation initiation. Alongside other techniques, such as western analysis and polysome profiling, toeprinting allows for a robust characterization of mechanisms for the regulation of translation initiation.

Toeprinting aims to measure the ability of in vitro transcribed RNA to form translation initiation complexes with ribosomes under a variety of conditions. This protocol describes a method for toeprinting mammalian RNA and can be used to study both cap-dependent and IRES-driven translation.

Translation initiation is the rate-limiting step of protein synthesis and represents a key point at which cells regulate their protein output. Regulation ...

Fluorescence Live-cell Imaging of the Complete Vegetative Cell Cycle of the Slow-growing Social Bacterium Myxococcus xanthus

Fluorescence live-cell imaging of bacterial cells is a key method in the analysis of the spatial and temporal dynamics of proteins and chromosomes underlying central cell cycle events. However, imaging of these molecules in slow-growing bacteria represents a challenge due to photobleaching of fluorophores and phototoxicity during image acquisition. Here, we describe a simple protocol to circumvent these limitations in the case of Myxococcus xanthus (which has a generation time of 4 - 6 h). To this end, M. xanthus cells are grown on a thick nutrient-containing agar pad in a temperature-controlled humid environment. Under these conditions, we determine the doubling time of individual cells by following the growth of single cells. Moreover, key cellular processes such as chromosome segregation and cell division can be imaged by fluorescence live-cell imaging of cells containing relevant fluorescently labeled marker proteins such as ParB-YFP, FtsZ-GFP, and mCherry-PomX over multiple cell cycles. Subsequently, the acquired images are processed to generate montages and/or movies.

Fluorescence Live-cell Imaging of the Complete Vegetative Cell Cycle of the Slow-growing Social Bacterium Myxococcus xanthus

Bacterial cells are spatially highly organized. To follow this organization over time in slow growing Myxococcus xanthus cells, a set-up for fluorescence live-cell imaging with high spatiotemporal resolution over several generations was developed. Using this method, spatiotemporal dynamics of important proteins for chromosome segregation and cell division could be determined.

Fluorescence live-cell imaging of bacterial cells is a key method in the analysis of the spatial and temporal dynamics of proteins and chromosomes ...

Human Peripheral Blood Neutrophil Isolation for Interrogating the Parkinson's Associated LRRK2 Kinase Pathway by Assessing Rab10 Phosphorylation

The leucine rich repeat kinase 2 (LRRK2) is the most frequently mutated gene in hereditary Parkinson&#8217; disease (PD) and all pathogenic LRRK2 mutations result in hyperactivation of its kinase function. Here, we describe an easy and robust assay to quantify LRRK2 kinase pathway activity in human peripheral blood neutrophils by measuring LRRK2-controlled phosphorylation of one of its physiological substrates, Rab10 at threonine 73. The immunoblotting analysis described requires a fully selective and phosphospecific antibody that recognizes the Rab10 Thr73 epitope phosphorylated by LRRK2, such as the MJFF-pRab10 rabbit monoclonal antibody. It uses human peripheral blood neutrophils, because peripheral blood is easily accessible and neutrophils are an abundant and homogenous constituent. Importantly, neutrophils express relatively high levels of both LRRK2 and Rab10. A potential drawback of neutrophils is their high intrinsic serine protease activity, which necessitates the use of very potent protease inhibitors such as the organophosphorus neurotoxin diisopropylfluorophosphate (DIFP) as part of the lysis buffer. Nevertheless, neutrophils are a valuable resource for research into LRRK2 kinase pathway activity in vivo and should be considered for inclusion into PD biorepository collections.

Mutations in the leucine rich repeat kinase 2 gene (LRRK2) cause hereditary Parkinson&#8217;s disease. We have developed an easy and robust method for assessing LRRK2-controlled phosphorylation of Rab10 in human peripheral blood neutrophils. This may help identify individuals with increased LRRK2 kinase pathway activity.

The leucine rich repeat kinase 2 (LRRK2) is the most frequently mutated gene in hereditary Parkinson&#8217; disease (PD) and all pathogenic LRRK2 ...

Application of Biolayer Interferometry (BLI) for Studying Protein-Protein Interactions in Transcription

A transcription factor&#160;(TF) is a protein that regulates gene expression by interacting with the RNA polymerase, another TF, and/or template DNA. GrgA is a novel transcription activator found specifically in the obligate intracellular bacterial pathogen Chlamydia. Protein pulldown assays using affinity beads have revealed that GrgA binds two &#963; factors, namely &#963;66 and &#963;28, which recognize different sets of promoters for genes whose products are differentially required at developmental stages. We have used BLI to confirm and further characterize the interactions. BLI demonstrates several advantages over pulldown: 1) It reveals real-time association and dissociation between binding partners, 2) It generates quantitative kinetic parameters, and 3) It can detect bindings that pulldown assays often fail to detect. These characteristics have enabled us to deduce the physiological roles of GrgA in gene expression regulation in Chlamydia, and possible detailed interaction mechanisms. We envision that this relatively affordable technology can be extremely useful for studying transcription and other biological processes.

Application of Biolayer Interferometry BLI for Studying Protein-Protein Interactions in Transcription

Interactions of transcription factors (TFs) with the RNA polymerase are usually studied using pulldown assays. We apply a Biolayer Interferometry (BLI) technology to characterize the interaction of GrgA with the chlamydial RNA polymerase. Compared to pulldown assays, BLI detects real-time association and dissociation, offers higher sensitivity, and is highly quantitative.

A transcription factor&#160;(TF) is a protein that regulates gene expression by interacting with the RNA polymerase, another TF, and/or template DNA. GrgA ...

Characterization at the Molecular Level using Robust Biochemical Approaches of a New Kinase Protein

Extensive whole genome sequencing has identified many Open Reading Frames (ORFs) providing many potential proteins. These proteins may have important roles for the cell and may unravel new cellular processes. Among proteins, kinases are major actors as they belong to cell signaling pathways and have the ability to switch on or off many processes crucial to the fate of the cell, such as cell growth, division, differentiation, motility, and death.
In this study, we focused on a new potential kinase protein, LIMK2-1. We demonstrated its existence by Western Blot using a specific antibody. We evaluated its interaction with an upstream regulating protein using coimmunoprecipitation experiments. Coimmunoprecipitation is a very powerful technique able to detect the interaction between two target proteins. It may also be used to detect new partners of a bait protein. The bait protein may be purified either via a tag engineered to its sequence or via an antibody specifically targeting it. These protein complexes may then be separated by SDS-PAGE (Sodium Dodecyl Sulfate PolyAcrylamide Gel) and identified using mass spectrometry. Immunoprecipitated LIMK2-1 was also used to test its kinase activity in vitro by &#947;[32P] ATP labeling. This well-established assay may use many different substrates, and mutated versions of the bait may be used to assess the role of specific residues. The effects of pharmacological agents may also be evaluated since this technique is both highly sensitive and quantitative. Nonetheless, radioactivity handling requires particular caution. Kinase activity may also be assessed with specific antibodies targeting the phospho group of the modified amino acid. These kinds of antibodies are not commercially available for all the phospho modified residues.

We characterized a new kinase protein using robust biochemical approaches: Western Blot analysis with a dedicated specific antibody on different cell lines and tissues, interactions by coimmunoprecipitation experiments, kinase activity detected by Western Blot using a phospho-specific antibody and by &#947;[32P] ATP labeling.

Extensive whole genome sequencing has identified many Open Reading Frames (ORFs) providing many potential proteins. These proteins may have important ...

Kinase Inhibitor Screening In Self-assembled Human Protein Microarrays

The screening of kinase inhibitors is crucial for better understanding properties of a drug and for the identification of potentially new targets with clinical implications. Several methodologies have been reported to accomplish such screening. However, each has its own limitations (e.g., the screening of only ATP analogues, restriction to using purified kinase domains, significant costs associated with testing more than a few kinases at a time, and lack of flexibility in screening protein kinases with novel mutations). Here, a new protocol that overcomes some of these limitations and can be used for the unbiased screening of kinase inhibitors is presented. A strength of this method is its ability to compare the activity of kinase inhibitors across multiple proteins, either between different kinases or different variants of the same kinase. Self-assembled protein microarrays generated through the expression of protein kinases by a human-based in vitro transcription and translation system (IVTT) are employed. The proteins displayed on the microarray are active, allowing for measurement of the effects of kinase inhibitors. The following procedure describes the protocol steps in detail, from the microarray generation and screening to the data analysis.

A detailed protocol for the generation of self-assembled human protein microarrays for the screening of kinase inhibitors is presented.

The screening of kinase inhibitors is crucial for better understanding properties of a drug and for the identification of potentially new targets with ...

Monitoring Protein-RNA Interaction Dynamics In Vivo at High Temporal Resolution Using &#967;CRAC

The interaction between RNA-binding proteins (RBPs) and their RNA substrates exhibits fluidity and complexity. Within its lifespan, a single RNA can be bound by many different RBPs that will regulate its production, stability, activity, and degradation. As such, much has been done to understand the dynamics that exist between these two types of molecules. A particularly important breakthrough came with the emergence of &#8216;cross-linking and immunoprecipitation&#8217; (CLIP). This technique allowed stringent investigation into which RNAs are bound by a particular RBP. In short, the protein of interest is UV cross-linked to its RNA substrates in vivo, purified under highly stringent conditions, and then the RNAs covalently cross-linked to the protein are converted into cDNA libraries and sequenced. Since its conception, many derivative techniques have been developed in order to make CLIP amenable to particular fields of study. However, cross-linking using ultraviolet light is notoriously inefficient. This results in extended exposure times that make the temporal study of RBP-RNA interactions impossible. To overcome this issue, we recently designed and built much-improved UV irradiation and cell harvesting devices. Using these new tools, we developed a protocol for time-resolved analyses of RBP-RNA interactions in living cells at high temporal resolution: Kinetic CRoss-linking and Analysis of cDNAs (&#967;CRAC). We recently used this technique to study the role of yeast RBPs in nutrient stress adaptation. This manuscript provides a detailed overview of the &#967;CRAC method and presents recent results obtained with the Nrd1 RBP.

Kinetic cross-linking and analysis of cDNA is a method that allows investigation of the dynamics of protein-RNA interactions in living cells at high temporal resolution. Here the protocol is described in detail, including the growth of yeast cells, UV cross-linking, harvesting, protein purification, and next generation sequencing library preparation steps.

The interaction between RNA-binding proteins (RBPs) and their RNA substrates exhibits fluidity and complexity. Within its lifespan, a single RNA can be ...