Name: toeprinting analysis of translation initiation complex formation on mammalian mrnas
Uploaded: 2018-05-10T13:00:00
Description: Watch this Scientific Journal Video about Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs at JoVE.com

This work was funded by a Natural Sciences and Engineering Research Council of Canada-Discovery Grant (RGPIN-2017-05463), the Canada Foundation for Innovation-John R. Evans Leaders Fund (35017), the Campus Alberta Innovates Program and the Alberta Ministry of Economic Development and Trade.

NOTE: RNA is highly susceptible to degradation by ribonucleases (RNases). Take standard precautions to keep the RNA intact. Change gloves frequently. Use filtered pipette tips, nuclease-free plasticware, and nuclease-free chemicals in all steps of the protocol. Use nuclease-free or diethyl pyrocarbonate (DEPC)-treated water for all solutions.
1. Preparation of Solutions
<ol>
	<li>Prepare Toeprinting buffer: 20 mM Tris-HCl (pH 7.6), 100 mM KOAc, 2.5 mM Mg(OAc)2, 5% (w/v) sucrose, 2...

<ol>
	<li>Holcik, 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=Translational+control+in+stress+and+apoptosis.">Translational control in stress and apoptosis.</a> Nat Rev Mol Cell Biol. 6 (4), 318-327 (2005).</li><li>Lacerda, R., Menezes, J., Romao, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=More+than+just+scanning:+the+importance+of+cap-independent+mRNA+translation+initiation+for+cellular+stress+response+and+cancer.">More than just scanning: the importance of cap-independent mRNA translation initiation for cellular stress response and cancer.</a> Cell Mol Life Sci. 74 (9), 1659-1680 (2017).</li><li>Sharma, D. K., Bressler, K., Patel, H., Balasingam, N., Thakor, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+Eukaryotic+Initiation+Factors+during+Cellular+Stress+and+Cancer+Progression.">Role of Eukaryotic Initiation Factors during Cellular Stress and Cancer Progression.</a> J Nucleic Acids. 2016, 8235121 (2016).</li><li>Gebauer, F., Hentze, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+mechanisms+of+translational+control.">Molecular mechanisms of translational control.</a> Nat Rev Mol Cell Biol. 5 (10), 827-835 (2004).</li><li>Anthony, D. D., Merrick, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+40+S+and+80+S+complexes+with+mRNA+as+measured+by+sucrose+density+gradients+and+primer+extension+inhibition.">Analysis of 40 S and 80 S complexes with mRNA as measured by sucrose density gradients and primer extension inhibition.</a> J Biol Chem. 267 (3), 1554-1562 (1992).</li><li>Hartz, D., McPheeters, D. S., Traut, R., Gold, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extension+inhibition+analysis+of+translation+initiation+complexes.">Extension inhibition analysis of translation initiation complexes.</a> Methods Enzymol. 164, 419-425 (1988).</li><li>Shirokikh, N. E., 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=Quantitative+analysis+of+ribosome-mRNA+complexes+at+different+translation+stages.">Quantitative analysis of ribosome-mRNA complexes at different translation stages.</a> Nucleic Acids Res. 38 (3), 15 (2010).</li><li>Thakor, N., Holcik, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=IRES-mediated+translation+of+cellular+messenger+RNA+operates+in+eIF2alpha-+independent+manner+during+stress.">IRES-mediated translation of cellular messenger RNA operates in eIF2alpha- independent manner during stress.</a> Nucleic Acids Res. 40 (2), 541-552 (2012).</li><li>Liwak, U., 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=Tumor+suppressor+PDCD4+represses+internal+ribosome+entry+site-mediated+translation+of+antiapoptotic+proteins+and+is+regulated+by+S6+kinase+2.">Tumor suppressor PDCD4 represses internal ribosome entry site-mediated translation of antiapoptotic proteins and is regulated by S6 kinase 2.</a> Mol Cell Biol. 32 (10), 1818-1829 (2012).</li><li>Thakor, N., 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=Cellular+mRNA+recruits+the+ribosome+via+eIF3-PABP+bridge+to+initiate+internal+translation.">Cellular mRNA recruits the ribosome via eIF3-PABP bridge to initiate internal translation.</a> RNA Biol. , 1-15 (2016).</li><li>Thoma, C., Bergamini, G., Galy, B., Hundsdoerfer, P., Hentze, M. W. <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+IRES-mediated+translation+of+the+c-myc+and+BiP+mRNAs+by+the+poly(A)+tail+is+independent+of+intact+eIF4G+and+PABP.">Enhancement of IRES-mediated translation of the c-myc and BiP mRNAs by the poly(A) tail is independent of intact eIF4G and PABP.</a> Mol Cell. 15 (6), 925-935 (2004).</li><li>Baird, S. D., Lewis, S. M., Turcotte, M., Holcik, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+search+for+structurally+similar+cellular+internal+ribosome+entry+sites.">A search for structurally similar cellular internal ribosome entry sites.</a> Nucleic Acids Res. 35 (14), 4664-4677 (2007).</li><li>Merrick, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+that+a+single+GTP+is+used+in+the+formation+of+80+S+initiation+complexes.">Evidence that a single GTP is used in the formation of 80 S initiation complexes.</a> J Biol Chem. 254 (10), 3708-3711 (1979).</li><li>Arnaud, E., 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+New+34-Kilodalton+Isoform+of+Human+Fibroblast+Growth+Factor+2+Is+Cap+Dependently+Synthesized+by+Using+a+Non-AUG+Start+Codon+and+Behaves+as+a+Survival+Factor.">A New 34-Kilodalton Isoform of Human Fibroblast Growth Factor 2 Is Cap Dependently Synthesized by Using a Non-AUG Start Codon and Behaves as a Survival Factor.</a> Mol Cell Biol. 19 (1), 505-514 (1999).</li><li>Dmitriev, S. E., Pisarev, A. V., Rubtsova, M. P., Dunaevsky, Y. E., Shatsky, I. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conversion+of+48S+translation+preinitiation+complexes+into+80S+initiation+complexes+as+revealed+by+toeprinting.">Conversion of 48S translation preinitiation complexes into 80S initiation complexes as revealed by toeprinting.</a> FEBS Lett. 533 (1-3), 99-104 (2003).</li><li>Faye, M. D., Graber, T. E., Holcik, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+selective+mRNA+translation+in+mammalian+cells+by+polysome+profiling.">Assessment of selective mRNA translation in mammalian cells by polysome profiling.</a> J Vis Exp. (92), e52295 (2014).</li><li>Duncan, C. D. S., Mata, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+cycloheximide+on+the+interpretation+of+ribosome+profiling+experiments+in+Schizosaccharomyces+pombe.">Effects of cycloheximide on the interpretation of ribosome profiling experiments in Schizosaccharomyces pombe.</a> Sci Rep. 7 (1), 10331 (2017).</li><li>Beck, H. J., Janssen, G. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+Translation+Initiation+Regulation+Mechanism+in+Escherichia+coli+ptrB+Mediated+by+a+5'-Terminal+AUG.">Novel Translation Initiation Regulation Mechanism in Escherichia coli ptrB Mediated by a 5'-Terminal AUG.</a> J Bacteriol. 199 (14), (2017).</li></ol>

Toeprinting is a powerful technique to directly measure the ability of an RNA of interest to support the formation of translation initiation complexes under highly controlled circumstances. This protocol describes a simplified technique for toeprinting mammalian RNAs. Rabbit reticulocyte lysate (RRL) is used as a convenient source of ribosomes, eIFs, initiator tRNA, and IRES trans-acting factors (ITAFs). The experimenter provides their RNA of choice, and can also supplement the toeprinting reaction with specific...

As translation consumes most cellular energy, it makes sense that translation is tightly regulated1. Conversely, dysregulation of translation-and the consequent alterations in protein output-is often observed in stress-response and disease states, such as cancer1,2. A major advantage of translational control is the speed with which cells can alter their protein output in order to respond to various stimuli3. Translation regulation thus represents an important mechanism that can influence cell survival and death1,2,3. Of the steps of translation, initiation is the most highly regulated and complex3. Briefly, most eukaryotic mRNAs contain a 5&#39; m7G cap that is almost always essential for their translation. Cap-dependent initiation requires eukaryotic initiation factors eIF4E, eIF4A, and eIF4G (the cap-recognition complex) to interact with the 5&#39; end of the mRNA. The 43S preinitiation ribosome complex, which contains eIF2-bound initiator tRNA and eIF3, is recruited to the 5&#39; end of the mRNA via an interaction of eIF4G with eIF3. The preinitiation complex is thought to scan mRNA, aided by eIF4A (an RNA helicase) until the start codon (AUG) is located. The 48S initiation complex is subsequently formed and tRNA is delivered into the P-site of the ribosome. Finally, the 60S and 40S ribosome subunits are united to form the 80S initiation complex, followed by translation elongation1,3,4. In contrast, internal ribosome entry sites (IRESes) bypass the requirement for a 5&#39; cap by recruiting the 40S ribosomal subunit directly to the initiation codon3. Physiological stress conditions attenuate global mRNA translation due to modifications of key general eukaryotic initiation factors (eIFs). However, non-canonical translation initiation mechanisms allow for selective translation of certain mRNAs which often encode stress-response proteins, and dysregulation of non-canonical translation initiation is implicated in disease states like cancer1,2. Discreet RNA regulatory elements, such as cellular IRESes, allow for the translation of such mRNAs2,3.
One particularly interesting aspect of translational control is to understand mechanisms of canonical versus non-canonical translation of a given mRNA. Toeprinting is a technique that allows the detailed mechanistic study of translation initiation of specific RNAs in vitro. The overall goal of toeprinting is to assess the ability of an RNA of interest to nucleate the formation of a translation initiation complex with the ribosome under a variety of conditions, in order to determine which sequences, structural elements, or accessory factors are required for efficient translation initiation. For instance, ribosome recruitment might be hindered in the absence of a 5&#39; cap but stimulated by the presence of an IRES.
The principle of the technique is to in vitro transcribe an RNA of interest, incubate it in the presence of cellular extracts containing translation components (or the purified components) to allow initiation complexes to form, and to reverse transcribe the RNA with a specific primer. Stable RNA-ribosome complexes will cause reverse transcription to stall at the 3&#39; edge of the ribosome-the so-called &#39;toeprint&#39;5,6,7.
In this protocol, the ribosomal subunits, eIFs, tRNAs, and IRES trans-acting factors (ITAFs) are conveniently contributed by rabbit reticulocyte lysate (RRL). Another advantage of this protocol is the use of a fluorescently-labeled primer and fluorescence gel-based imager, rather than a radiolabeled primer. This eliminates extra steps, including radiolabeling the primer, as well as drying the gel and exposing it to an intensifying screen. The fluorescent bands are recorded in real time, as the gel runs, allowing for greater resolution. Uncapped X-linked inhibitor of apoptosis protein (XIAP) IRES RNA is used as an example here, although capped mRNAs can also be analyzed by this technique8.
Unlike western analysis, which measures the final output of the translation process in cell lysates, toeprinting is an in vitro approach to measure translation initiation complex formation on an RNA. This reductionist approach allows for the highly detailed study of substrates or factors that regulate translation initiation (e.g., capped or un-capped mRNA, IRES structure, presence or absence of poly-A tail, provision of specific protein factors, etc.). Hence, toeprinting can be used to study different modes of translation8 or the effects of mRNA structures, such as IRESes, on protein synthesis9,10.

<table border="0" cellpadding="0" cellspacing="0" style="width:1045px;" width="1043">
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	<tbody>
		<tr height="40">
			<td height="40" style="height:40px;width:405px;">DEPC (Diethyl pyrocarbonate)</td>
			<td style="width:159px;">Sigma</td>
			<td style="width:191px;">D5758-100ML</td>
			<td style="width:291px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">TRIS base, Ultrapure</td>
			<td>JT Baker</td>
			<td>4109-01</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">KOAc (Potassium acetate)</td>
			<td>Bio Basic</td>
			<td>PB0438</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Mg(OAc)2 (Magnesium acetate tetrahydrate)</td>
			<td>Bio Basic</td>
			<td>MB0326</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Sucrose, molecular biology grade</td>
			<td>Calbiochem</td>
			<td>573113-1KG</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Spermidine</td>
			<td>Sigma</td>
			<td>85558</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">GMP-PNP (Guanosine 5&#8242;-[&#946;,&#947;-imido]triphosphate trisodium salt hydrate) 0.1 M solution</td>
			<td>Sigma</td>
			<td>G0635</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">ATP (Adenosine 5&#8242;-triphosphate) disodium salt, 100 mM solution</td>
			<td>Sigma</td>
			<td>A6559</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">19:1 Acrylamide:bis-acrylamide, 40%</td>
			<td>Bio Basic</td>
			<td>A0006</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Urea</td>
			<td>Bio Basic</td>
			<td>UB0148</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">500mL bottle top filtration units, 0.2 &#181;m</td>
			<td>Sarstedt</td>
			<td>83.1823.101</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Formamide</td>
			<td>Sigma</td>
			<td>F9037-100ML</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">EDTA (disodium salt, dihydrate)</td>
			<td>Bio Basic</td>
			<td>EB0185</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">SDS</td>
			<td>Bio Basic</td>
			<td>SB0485</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Bromophenol blue</td>
			<td>Bio Basic</td>
			<td>BDB0001</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Xylene cyanol FF</td>
			<td>Bio Basic</td>
			<td>XB0005</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">MEGAshortscript T7 transcription kit</td>
			<td>Ambion</td>
			<td>AM1354</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">mMESSAGE mMACHINE T7 transcription kit</td>
			<td>Ambion</td>
			<td>AM1344</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Acid Phenol:Chloroform (5:1)</td>
			<td>Ambion</td>
			<td>AM9722</td>
			<td></td>
		</tr>
		<tr height="33">
			<td height="33" style="height:33px;width:405px;">25:24:1 Phenol:Chloroform:Isoamyl Alcohol</td>
			<td style="width:159px;">Invitrogen</td>
			<td style="width:191px;">15593-049</td>
			<td style="width:291px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Rabbit Reticulocyte Lysate (RRL). Should NOT be nuclease-treated.</td>
			<td>Green Hectares, USA</td>
			<td></td>
			<td>Contact Green Hectares, ask for 1:1 RRL:water</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">RiboLock RNase Inhibitor (40 U/&#181;L)</td>
			<td>Thermo Fisher</td>
			<td>E00382</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">100 mM dNTPs</td>
			<td>Invitrogen</td>
			<td>56172, 56173, 56174, 56175</td>
			<td>Mix equal parts for a stock of 25 mM each.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">AMV-RT, 10 U/&#181;L</td>
			<td>Promega</td>
			<td>M5101</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Sequenase Version 2.0 DNA Sequencing Kit</td>
			<td>Thermo Fisher</td>
			<td>707701KT</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Model 4200 IR2 DNA analyzer</td>
			<td>LI-COR</td>
			<td></td>
			<td>Product has been discontinued</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">APS (Ammonium Persulfate)</td>
			<td>Bio Basic</td>
			<td>AB0072</td>
			<td></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">TEMED</td>
			<td>Bio Basic</td>
			<td>TB0508</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:405px;">Phusion High Fidelity Polymerase</td>
			<td style="width:159px;">New England Biolabs</td>
			<td style="width:191px;">M0530</td>
			<td style="width:291px;"></td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;">Turbo Dnase</td>
			<td>Thermo Fisher</td>
			<td>AM2238</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

We have previously described the ability of the XIAP IRES to support cap-independent translation initiation in vitro8,10. Toeprinting was the key technique to interrogate the mechanistic details of the XIAP IRES initiation complex. A DNA construct encoding an mRNA containing the XIAP IRES (Figure 1A) was in vitro transcribed and subjected to toeprinting analysis. The...

Watch this Scientific Journal Video about Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs at JoVE.com

Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs

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 ...

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