We wish to thank all of the members of the Dinman laboratory, including Ashton Belew, Karen Jack, Sharmishtha Musalga, Sergey Sulima, Shivani Reddy, and Michael Rhodin for their help and input on this project. This work was supported by grants to AM from the American Heart Association (AHA 0630163N) and to JDD from the National Institutes of Health (5R01 GM058859-12). JAL was supported by an American Reinvestment and Recovery Act of 2009 supplement to the parent grant (3R01GM058859-11S1).

1. Preparation of a cysteine charged Sulfolink resin
<ol>
<li>Prepare Sulfolink resin (Pierce) at room temperature.</li>
<li>Place a total of 10 ml of a 50% slurry of Sulfolink coupling gel as supplied by the manufacturer in two 10 ml plastic vials, with 5 ml distributed into each vial.</li>
<li>Briefly centrifuge vials at 850 x g and carefully remove supernatants.</li>
<li>Wash the gel three times in coupling buffer (50 mM Tris, pH 8.5, 5 mM EDTA) by resuspending the beads in 5 ml, centrifuging briefly at 850 x g and removing the supernatant by pipette.</li>
<li>Add five ml of a 50 mM solution of L-cysteine in coupling buffer to each tube and mix the slurry for 1 hour at 25&deg;C.</li>
<li>Remove the residual L-cysteine by washing as described in step 1.4 above.</li>
<li>Resuspend the gel in 10 ml of binding buffer [20 mM HEPES, pH 7.6, 5 mM Mg(OAc)2, 60 mM NH4Cl, 2 mM DTT], and equilibrate the resin by washing in 10 ml of binding buffer 3 times as described in step 1.4. Decant resin into a 10 ml centrifuge column, cap and stored at 4&deg;C. The resin capacity for RNA binding is &tilde;20 A260 units per ml.</li>
</ol>
 2. Chromatographic purification of ribosomes using a cysteine charged Sulfolink resin
Note: If working with a strain where protease activity proves to be an issue, protease inhibition cocktails can be used in all subsequent buffers.
<ol>
<li>Maintain all components on ice and prepare all solutions using RNase-free water and sterile filtration.</li>
<li>Grow yeast cells overnight to mid-log phase (O.D.595 = 0.6 - 1.2) in appropriate media. Pellet cells by centrifugation, and wash 1 gram cells in binding buffer and centrifuge at 3700 x g for 5 minutes at 4&deg;C.</li>
<li>Resuspend cells in 1 ml of binding buffer to an approximate total volume of 2 ml, and disrupt using an equal volume of 0.5 mm glass beads chilled to 4&deg;C using a Biospec Mini-bead beater (Bartlesville, OK). Samples can be split into multiple tubes as needed.</li>
<li>Remove unbroken cells, organelles, and cellular debris by centrifugation at 30,000 x g for 30 minutes in a Beckman-Coulter Optima Max E ultracentrifuge (Fullerton, CA). </li>
<li>Immediately before use, pellet the resin for one minute at 1,000 x g to remove the storage solution. Two ml of resin is used for every one gram of cells.</li>
<li>Remove cell lysate supernatants from the 30,000 x g spin (S30), taking care to minimize contamination from either the lipid fraction at the very top or the cell debris at the bottom of the tubes, and place directly into the charged Sulfolink slurry. The lipid layer can be avoided either by removal or by pushing out from the pipet after the tip has crossed into the supernatant.</li>
<li>Incubate the S30/Sulfolink mixture on ice without mixing for 15 minutes.</li>
<li>Place the columns into 15 ml conical tubes and centrifuge at 1,000 x g for one minute.</li>
<li>Place the flowthrough fractions back into the columns, mix by hand, and incubate for a further 15 minutes on ice.</li>
<li>Place the columns into 15 ml conical tubes and centrifuge at 1,000 x g for one minute. Discard the flowthrough.</li>
<li>Cap columns and add 5 ml of binding buffer. Mix columns by hand until resuspended, remove the caps, and centrifuge the columns centrifuge at 1,000 x g for one minute. Repeat this washing protocol two more times.</li>
<li>Add 1.5 ml of elution buffer (20 mM HEPES-KOH, pH 7.6, 10 mM Mg(OAc)2, 500 mM KCl, 2mM DTT, 0.5 mg/ml heparin) to each column. Mix slurries by hand, and incubate on ice for 2 minutes</li>
<li>Place columns into new 15 ml conical tubes and centrifuge at 1,000 x g for 1 minute. Collect eluate. Repeat the elution step once more so that the final combined sample volumes are &tilde; 3 ml. Used resin can be washed with elution buffer without heparin and followed by equilibration with binding buffer, and stored in 10 ml volumes of binding buffer at 4&deg;C for re-use later.</li>
</ol>
3. Puromycin treatment
Note: An alternative method to remove contaminating tRNA species is to switch from a glucose rich to glucose depleted media to promote ribosome runoff. However, this does change the metabolic status of the yeast cells, which could affect ribosome function and concentration.
In order to strip the ribosomes from endogenous peptidyl-tRNA, a treatment with puromycin is performed.
<ol>
<li>Neutralize to pH 7.5 100 mM puromycin solution by adding 1M KOH dropwise at room temperature.</li>
<li>Add neutralized puromycin solution to &tilde; 1mM final concentration in eluate.</li>
<li>Add 100 mM GTP to a final concentration of 1 mM.</li>
<li>Incubate for 30 minutes at 30&deg;C.</li>
</ol>
4. Purification of ribosomes by sedimentation through glycerol cushions
<ol>
<li>Place one ml of cushion buffer (20 mM HEPES, pH 7.6, 10 mM Mg(OAc)2, 500 mM KCl, 2 mM DTT, 25% glycerol) into a 4 ml volume polycarbonate ultracentrifuge tube.</li>
<li>Gently layer puromycin treated elution fractions on top of the cushion, and centrifuge samples at 100,000 x g overnight at 4&deg;C.</li>
<li>Remove tubes from the centrifuge rotor, and aspirate supernatants.</li>
<li>Wash pellets containing purified ribosomes twice with 1 ml of cushion buffer.</li>
<li>Resuspend ribosomes in 100 &mu;l of cushion buffer by gentle disruption using a glass rod.</li>
<li>After disruption, cover tubes with parafilm and shake at a moderate speed in a cold room vortex for one hour.</li>
<li>Transfer the contents to a microcentrifuge tube, centrifuge for 5 minutes at maximum speed at 4&deg;C, and remove supernatants to fresh tubes.</li> 
<li>Repeat steps 4.1 to 4.7 using 2 ml of cushion buffer and, except that 100 &mu;l of storage buffer (50 mM HEPES -KOH pH 7.6, 50 mM NH4Cl, 5 mM Mg(OAc)2, 1 mM DTT, 25% glycerol) is used in steps 4.4 and 4.5 instead of cushion buffer.</li>
<li>Quantify the purified ribosomes spectrophotometrically (1 A260 = 20 pmoles of yeast ribosomes), and store at -80&deg;C. Typical results from 1 gram of yeast are 300-400 pmoles of ribosomes.</li>
</ol>
5. Representative results: 
An example of RNA species extracted from each of the three major steps of the protocol is shown in Figure 2. While rRNAs are the major species present in total cell lysates (T) these also contain a large number of other RNA species. Ribosomes purified from the Sulfolink column (SL) also contain a large amount of tRNAs due to the high affinity of the column bed for these species as well. Treatment of this fraction with puromycin results in hydrolysis of peptides from peptidyl-tRNAs, and promotes dissociation of these species from ribosomes. The puromycin treated samples (Pm) lack co-purifying tRNA species, and thus represent completely pure ribosomes. As previously reported8, these ribosomes are highly intact and biochemically active, making them ideal substrates for detailed functional and structural analyses.
<img src="/files/ftp_upload/3214/3214fig1.jpg" alt="Figure 1"/> Figure 1. Method Flowchart. Chromatographic purification of ribosomes using the cysteine linked sulfolink resin is depicted.
<img src="/files/ftp_upload/3214/3214fig2.jpg" alt="Figure 2"/> Figure 2. Representative analysis of ribosome preparations. Total RNA species were extracted from total cell lysates (T), Sulfolink purified ribosomes (SL) and Sulfolink purified ribosomes subsequently treated with puromycin and sedimented through a glycerol cushion (Pm). Lane M represents RNA size markers. Bands representing 25S and 18S rRNAs, as well as tRNAs and other RNA species are indicated. All lanes were loaded with 2 &mu;g of RNA.

<ol>
	<li>Palade, G. E., Siekevitz, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liver+microsomes;+an+integrated+morphological+and+biochemical+study.">Liver microsomes; an integrated morphological and biochemical study.</a> J. Biophys. Biochem. Cytol. 2, 171-200 (1956).</li><li>Fabry, M., Kalvoda, L., Rychlik, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrophobic+interactions+of+Escherichia+coli+ribosomes.">Hydrophobic interactions of Escherichia coli ribosomes.</a> Biochim. Biophys. Acta. 652, 139-150 (1981).</li><li>Jelenc, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+purification+of+highly+active+ribosomes+from+Escherichia+coli.">Rapid purification of highly active ribosomes from Escherichia coli.</a> Anal. Biochem. 105, 369-374 (1980).</li><li>Le goffic, F., Moreau, N., Chevelot, L., Langrene, S., Siegrist, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Purification+of+bacterial+ribosomes+using+chloramphenicol+and+erythromycin+columns.">Purification of bacterial ribosomes using chloramphenicol and erythromycin columns.</a> Biochimie. 62, 69-77 (1980).</li><li>Meskauskas, A., Petrov, A. N., Dinman, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+functionally+important+amino+acids+of+ribosomal+protein+L3+by+saturation+mutagenesis.">Identification of functionally important amino acids of ribosomal protein L3 by saturation mutagenesis.</a> Mol. Cell Biol. 25, 10863-10874 (2005).</li><li>Algire, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+and+characterization+of+a+reconstituted+yeast+translation+initiation+system.">Development and characterization of a reconstituted yeast translation initiation system.</a> RNA. 8, 382-397 (2002).</li><li>Maguire, B. A., Wondrack, L. M., Contillo, L. G., Xu, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+chromatography+system+to+isolate+active+ribosomes+from+pathogenic+bacteria.">A novel chromatography system to isolate active ribosomes from pathogenic bacteria.</a> RNA. 14, 188-195 (2008).</li><li>Leshin, J. A., Rakauskaite, R., Dinman, J. D., Meskauskas, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+purity,+activity+and+structural+integrity+of+yeast+ribosomes+purified+using+a+general+chromatographic+method.">Enhanced purity, activity and structural integrity of yeast ribosomes purified using a general chromatographic method.</a> RNA. Biol. 7, 354-360 (2010).</li><li>Triana, F., Nierhaus, K. H., Chakraburtty, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transfer+RNA+binding+to+80S+ribosomes+from+yeast:+evidence+for+three+sites.">Transfer RNA binding to 80S ribosomes from yeast: evidence for three sites.</a> Biochem. Mol. Biol. Int. 33, 909-915 (1994).</li><li>Azzam, M. E., Algranati, I. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanism+of+puromycin+action:+fate+of+ribosomes+after+release+of+nascent+protein+chains+from+polysomes.">Mechanism of puromycin action: fate of ribosomes after release of nascent protein chains from polysomes.</a> Proc. Natl. Acad. Sci. U. S. A. 70, 3866-3869 (1973).</li><li>Nathans, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Puromuycin+inhibition+of+protein+synthesis:+incorporation+of+puromycin+into+peptide+chains.">Puromuycin inhibition of protein synthesis: incorporation of puromycin into peptide chains.</a> Proc. Natl. Acad. Sci. U. S. A. 51, 585-592 (1964).</li><li>Rabinovitz, M., Fisher, J. 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+dissociative+effect+of+puromycin+on+the+pathway+of+protein+synthesis+by+Ehrlich+ascites+tumor+cells.">A dissociative effect of puromycin on the pathway of protein synthesis by Ehrlich ascites tumor cells.</a> J. Biol. Chem. 237, 477-481 (1962).</li><li>Allen, D. W., Zamecnik, P. 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+effect+of+puromycin+on+rabbit+reticulocyte+ribosomes.">The effect of puromycin on rabbit reticulocyte ribosomes.</a> Biochim. Biophys. Acta. 55, 865-874 (1962).</li><li>Yarmolinsky, M. B., Haba, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibition+by+puromycin+of+amino+acid+incorporation+into+protein.">Inhibition by puromycin of amino acid incorporation into protein.</a> Proc. Natl. Acad. Sci. U. S. A. 45, 1721-1729 (1959).</li><li>Becker-Ursic, D., Davies, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+and+in+vitro+phosphorylation+of+ribosomal+proteins+by+protein+kinases+from+Saccharomyces+cerevisiae.">In vivo and in vitro phosphorylation of ribosomal proteins by protein kinases from Saccharomyces cerevisiae.</a> Biochemistry. 15, 2289-2296 (1976).</li></ol>

No conflicts of interest declared.

Ribosome purification protocols basically involve lysing cells, harvesting a cytosolic fraction from a low speed spin, and then pelleting ribosomes by high speed centrifugation 1. While a few novel methods have been used for purifying bacterial ribosomes, the same had not been true for eukaryotes 2-4. Although additional steps have been added along the years, e.g. salt washes, and glycerol cushions (e.g. see 5), biochemical and structural studies of yeast ribosomes have been hampered by ...

<table border="1">
	<tbody>
		<tr>
			<td>Name of the reagent</td>
			<td>Company</td>
			<td>Catalogue number</td>
		</tr>
		<tr>
			<td>Sulfolink Coupling resin</td>
			<td>Pierce</td>
			<td>20402</td>
		</tr>
		<tr>
			<td>Mini bead-beater 16</td>
			<td>Biospec</td>
			<td>607</td>
		</tr>
		<tr>
			<td>Optima Max E ultracentrifuge</td>
			<td>Beckman Coulter</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Legend RT</td>
			<td>Sorvall</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>0.5 mm Glass beads</td>
			<td>Biospec</td>
			<td>11079105</td>
		</tr>
		<tr>
			<td>Tris</td>
			<td>Sigma-Aldrich</td>
			<td>252859</td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>Sigma-Aldrich</td>
			<td>E9884</td>
		</tr>
		<tr>
			<td>DTT</td>
			<td>Sigma-Aldrich</td>
			<td>43815</td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Sigma-Aldrich</td>
			<td>54459</td>
		</tr>
		<tr>
			<td>NH4Cl</td>
			<td>Sigma-Aldrich</td>
			<td>A9434</td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma-Aldrich</td>
			<td>60128</td>
		</tr>
		<tr>
			<td>Mg(OAc)2</td>
			<td>Sigma-Aldrich</td>
			<td>M5661</td>
		</tr>
		<tr>
			<td>KOH	</td>
			<td>Sigma-Aldrich</td>
			<td>221473</td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Sigma-Aldrich</td>
			<td>G5516</td>
		</tr>
		<tr>
			<td>Puromycin</td>
			<td>Sigma-Aldrich</td>
			<td>P7255</td>
		</tr>
		<tr>
			<td>GTP</td>
			<td>Fermentas</td>
			<td>R0461</td>
		</tr>
	</tbody>
</table>

chromatographic purification of highly active yeast ribosomes

Eukaryotic ribosomes are much more labile as compared to their eubacterial and archael counterparts, thus posing a significant challenge to researchers. Particularly troublesome is the fact that lysis of cells releases a large number of proteases and nucleases which can degrade ribosomes. Thus, it is important to separate ribosomes from these enzymes as quickly as possible. Unfortunately, conventional differential ultracentrifugation methods leaves ribosomes exposed to these enzymes for unacceptably long periods of time, impacting their structural integrity and functionality. To address this problem, we utilize a chromatographic method using a cysteine charged Sulfolink resin. This simple and rapid application significantly reduces co-purifying proteolytic and nucleolytic activities, producing high yields of intact, highly biochemically active yeast ribosomes. We suggest that this method should also be applicable to mammalian ribosomes. The simplicity of the method, and the enhanced purity and activity of chromatographically purified ribosome represents a significant technical advancement for the study of eukaryotic ribosomes.

Watch this Scientific Journal Video about Chromatographic Purification of Highly Active Yeast Ribosomes at JoVE.com

Chromatographic Purification of Highly Active Yeast Ribosomes

Contamination of preparations of eukaryotic ribosomes purified by traditional methods by co-purifying nucleases and proteases negatively impacts on downstream biochemical and structural analyses. A rapid and simple chromatographic purification method is used to solve this problem using yeast ribosomes as a model system.

Eukaryotic ribosomes are much more labile as compared to their eubacterial and archael counterparts, thus posing a significant challenge to researchers.  ...

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16.7K Views.  University of Maryland. Contamination of preparations of eukaryotic ribosomes purified by traditional methods by co-purifying nucleases and proteases negatively impacts on downstream biochemical and structural analyses. A rapid and simple chromatographic purification method is used to solve this problem using yeast ribosomes as a model system.

Video: Chromatographic Purification of Highly Active Yeast Ribosomes

Staining of Proteins in Gels with Coomassie G-250 without Organic Solvent and Acetic Acid

In classical protein staining protocols using Coomassie Brilliant Blue (CBB), solutions with high contents of toxic and flammable organic solvents (Methanol, Ethanol or 2-Propanol) and acetic acid are used for fixation, staining and destaining of proteins in a gel after SDS-PAGE. To speed up the procedure, heating the staining solution in the microwave oven for a short time is frequently used. This usually results in evaporation of toxic or hazardous Methanol, Ethanol or 2-Propanol and a strong smell of acetic acid in the lab which should be avoided due to safety considerations. In a protocol originally published in two patent applications by E.M. Wondrak (US2001046709 (A1), US6319720 (B1)), an alternative composition of the staining solution is described in which no organic solvent or acid is used. The CBB is dissolved in bidistilled water (60-80mg of CBB G-250 per liter) and 35 mM HCl is added as the only other compound in the staining solution. The CBB staning of the gel is done after SDS-PAGE and thorough washing of the gel in bidistilled water. By heating the gel during the washing and staining steps, the process can be finished faster and no toxic or hazardous compunds are evaporating. The staining of proteins occurs already within 1 minute after heating the gel in staining solution and is fully developed after 15-30 min with a slightly blue background that is destained completely by prolonged washing of the stained gel in bidistilled water, without affecting the stained protein bands.

A short protocol for protein staining with Coomassie Brilliant Blue (CBB) G-250 in polyacrylamide gels is described without using organic solvents or acetic acid as in the classical staining procedures with CBB.

In classical protein staining protocols using Coomassie Brilliant Blue (CBB), solutions with high contents of toxic and flammable organic solvents ...

Purification of Mitochondria from Yeast Cells

Mitochondria are the main site of ATP production during aerobic metabolism in eukaryotic non-photosynthetic cells1. These complex organelles also play essential roles in apoptotic cell death2, cell survival3, mammalian development4, neuronal development and function4, intracellular signalling5, and longevity regulation6. Our understanding of these complex biological processes controlled by mitochondria relies on robust methods for assessing their morphology, their protein and lipid composition, the integrity of their DNA, and their numerous vital functions. The budding yeast Saccharomyces cerevisiae, a genetically and biochemically manipulable unicellular eukaryote with annotated genome and well-defined proteome, is a valuable model for studying the molecular and cellular mechanisms underlying essential biological functions of mitochondria. For these types of studies, it is crucial to have highly pure mitochondria. Here we present a detailed description of a rapid and effective method for purification of yeast mitochondria. This method enables the isolation of highly pure mitochondria that are essentially free of contamination by other organelles and retain their structural and functional integrity after their purification. Mitochondria purified by this method are suitable for cell-free reconstitution of essential mitochondrial processes and can be used for the analysis of mitochondrial structure and functions, mitochondrial proteome and lipidome, and mitochondrial DNA.

We describe a rapid and effective method for purification of mitochondria from the yeast Saccharomyces cerevisiae. This method enables the high-yield isolation of pure mitochondria that are essentially free of contamination by other organelles and retain their structural and functional integrity after their purification.

Mitochondria are the main site of ATP production during aerobic metabolism in eukaryotic non-photosynthetic cells1. These complex organelles also play ...

Preparation of Highly Coupled Rat Heart Mitochondria

The function of mitochondria in generation of cellular ATP in the process of oxidative phosphorylation is widely recognised. During the past decades there have been significant advances in our understanding of the functions of mitochondria other than the generation of energy. These include their role in apoptosis, acting as signalling organelles, mammalian development and ageing as well as their contribution to the coordination between cell metabolism and cell proliferation. Our understanding of biological processes modulated by mitochondria is based on robust methods for isolation and handling of intact mitochondria from tissues of the laboratory animals. Mitochondria from rat heart is one of the most common preparations for past and current studies of cellular metabolism including studies on knock-out animals.
Here we describe a detailed rapid method for isolation of intact mitochondria with a high degree of coupling. Such preparation of rat heart mitochondria is an excellent object for functional and structural research on cellular bioenergetics, transport of biomolecules, proteomic studies and analysis of mitochondrial DNA, proteins and lipids.

We describe &#1072; protocol for isolation of pure, highly coupled rat heart mitochondria for functional or structural studies of cellular bioenergetics, biophysical measurements, proteomics or mitochondrial DNA and lipids analysis.

The function of mitochondria in generation of cellular ATP in the process of oxidative phosphorylation is widely recognised. During the past decades there ...

Isolation of Translating Ribosomes Containing Peptidyl-tRNAs for Functional and Structural Analyses

Recently, structural and biochemical studies have detailed many of the molecular events that occur in the ribosome during inhibition of protein synthesis by antibiotics and during nascent polypeptide synthesis. Some of these antibiotics, and regulatory nascent polypeptides mostly in the form of peptidyl-tRNAs, inhibit either peptide bond formation or translation termination1-7. These inhibitory events can stop the movement of the ribosome, a phenomenon termed "translational arrest". Translation arrest induced by either an antibiotic or a nascent polypeptide has been shown to regulate the expression of genes involved in diverse cellular functions such as cell growth, antibiotic resistance, protein translocation and cell metabolism8-13. Knowledge of how antibiotics and regulatory nascent polypeptides alter ribosome function is essential if we are to understand the complete role of the ribosome in translation, in every organism.
Here, we describe a simple methodology that can be used to purify, exclusively, for analysis, those ribosomes translating a specific mRNA and containing a specific peptidyl-tRNA14. This procedure is based on selective isolation of translating ribosomes bound to a biotin-labeled mRNA. These translational complexes are separated from other ribosomes in the same mixture, using streptavidin paramagnetic beads (SMB) and a magnetic field (MF). Biotin-labeled mRNAs are synthesized by run-off transcription assays using as templates PCR-generated DNA fragments that contain T7 transcriptional promoters. T7 RNA polymerase incorporates biotin-16-UMP from biotin-UTP; under our conditions approximately ten biotin-16-UMP molecules are incorporated in a 600 nt mRNA with a 25% UMP content. These biotin-labeled mRNAs are then isolated, and used in in vitro translation assays performed with release factor 2 (RF2)-depleted cell-free extracts obtained from Escherichia coli strains containing wild type or mutant ribosomes. Ribosomes translating the biotin-labeled mRNA sequences are stalled at the stop codon region, due to the absence of the RF2 protein, which normally accomplishes translation termination. Stalled ribosomes containing the newly synthesized peptidyl-tRNA are isolated and removed from the translation reactions using SMB and an MF. These beads only bind biotin-containing messages.
The isolated, translational complexes, can be used to analyze the structural and functional features of wild type or mutant ribosomal components, or peptidyl-tRNA sequences, as well as determining ribosome interaction with antibiotics or other molecular factors 1,14-16. To examine the function of these isolated ribosome complexes, peptidyl-transferase assays can be performed in the presence of the antibiotic puromycin1. To study structural changes in translational complexes, well established procedures can be used, such as i) crosslinking to specific amino acids14 and/or ii) alkylation protection assays1,14,17.

A major impediment to biochemical analyses of ribosomes containing nascent peptidyl-tRNAs has been the presence of other ribosomes in the same samples, ribosomes not involved in the translation of the specific mRNA sequence being analyzed. We developed a simple methodology to purify, exclusively, the ribosomes containing the nascent peptidyl-tRNA of interest.

Recently, structural and biochemical studies have detailed many of the molecular events that occur in the ribosome during inhibition of protein synthesis ...

Yeast Colony Embedding Method

Patterning of different cell types in embryos is a key mechanism in metazoan development. Communities of microorganisms, such as colonies and biofilms also display patterns of cell types. For example, in the yeast S. cerevisiae, sporulated cells and pseudohyphal cells are not uniformly distributed in colonies. The functional importance of patterning and the molecular mechanisms that underlie these patterns are still poorly understood.
One challenge with respect to investigating patterns of cell types in fungal colonies is that unlike metazoan tissue, cells in colonies are relatively weakly attached to one another. In particular, fungal colonies do not contain the same extensive level of extracellular matrix found in most tissues . Here we report on a method for embedding and sectioning yeast colonies that reveals the interior patterns of cell types in these colonies. The method can be used to prepare thick sections (0.5 &mu;) useful for light microscopy and thin sections (0.1 &mu;) suitable for transmission electron microscopy. Asci and pseudohyphal cells can easily be distinguished from ovoid yeast cells by light microscopy , while the interior structure of these cells can be visualized by EM.
The method is based on surrounding colonies with agar, infiltrating them with Spurr's medium, and then sectioning. Colonies with a diameter in the range of 1-2 mm are suitable for this protocol. In addition to visualizing the interior of colonies, the method allows visualization of the region of the colony that invades the underlying agar.

A method for embedding yeast colonies allowing sectioning for light and electron microscopy. This protocol allows determination of the distribution of sporulated cells and pseudohyphal cells within colonies providing a new tool toward understanding the organization of cell types within a fungal community.

Patterning of  different cell types in embryos is a key mechanism in metazoan development. Communities of microorganisms, such as colonies and biofilms ...

In vitro Reconstitution of the Active T. castaneum Telomerase

Efforts to isolate the catalytic subunit of telomerase, TERT, in sufficient quantities for structural studies, have been met with limited success for more than a decade. Here, we present methods for the isolation of the recombinant Tribolium castaneum TERT (TcTERT) and the reconstitution of the active T. castaneum telomerase ribonucleoprotein (RNP) complex in vitro.
Telomerase is a specialized reverse transcriptase1 that adds short DNA repeats, called telomeres, to the 3' end of linear chromosomes2 that serve to protect them from end-to-end fusion and degradation. Following DNA replication, a short segment is lost at the end of the chromosome3 and without telomerase, cells continue dividing until eventually reaching their Hayflick Limit4. Additionally, telomerase is dormant in most somatic cells5 in adults, but is active in cancer cells6 where it promotes cell immortality7.
The minimal telomerase enzyme consists of two core components: the protein subunit (TERT), which comprises the catalytic subunit of the enzyme and an integral RNA component (TER), which contains the template TERT uses to synthesize telomeres8,9. Prior to 2008, only structures for individual telomerase domains had been solved10,11. A major breakthrough in this field came from the determination of the crystal structure of the active12, catalytic subunit of T. castaneum telomerase, TcTERT1.
Here, we present methods for producing large quantities of the active, soluble TcTERT for structural and biochemical studies, and the reconstitution of the telomerase RNP complex in vitro for telomerase activity assays. An overview of the experimental methods used is shown in Figure 1.

In vitro Reconstitution of the Active T. castaneum Telomerase

Efforts to isolate the catalytic subunit of telomerase, TERT, in sufficient quantities for structural studies, have been met with limited success for more than a decade. Here, we present methods for the isolation of the recombinant Tribolium castaneum TERT (TcTERT) and the reconstitution of the active T. castaneum telomerase ribonucleoprotein (RNP) complex in vitro.

Efforts to isolate the catalytic subunit of telomerase, TERT, in sufficient quantities for structural studies, have been met with limited success for more ...

High-throughput Yeast Plasmid Overexpression Screen

The budding yeast, Saccharomyces cerevisiae, is a powerful model system for defining fundamental mechanisms of many important cellular processes, including those with direct relevance to human disease. Because of its short generation time and well-characterized genome, a major experimental advantage of the yeast model system is the ability to perform genetic screens to identify genes and pathways that are involved in a given process. Over the last thirty years such genetic screens have been used to elucidate the cell cycle, secretory pathway, and many more highly conserved aspects of eukaryotic cell biology 1-5. In the last few years, several genomewide libraries of yeast strains and plasmids have been generated 6-10. These collections now allow for the systematic interrogation of gene function using gain- and loss-of-function approaches 11-16. Here we provide a detailed protocol for the use of a high-throughput yeast transformation protocol with a liquid handling robot to perform a plasmid overexpression screen, using an arrayed library of 5,500 yeast plasmids. We have been using these screens to identify genetic modifiers of toxicity associated with the accumulation of aggregation-prone human neurodegenerative disease proteins. The methods presented here are readily adaptable to the study of other cellular phenotypes of interest.

Here we describe a plasmid overexpression screen in Saccharomyces cerevisiae, using an arrayed plasmid library and a high-throughput yeast transformation protocol with a liquid handling robot.

The budding yeast, Saccharomyces cerevisiae, is a powerful model system for defining fundamental mechanisms of many important cellular processes, ...

Competitive Genomic Screens of Barcoded Yeast Libraries

By virtue of advances in next generation sequencing technologies, we have access to new genome sequences almost daily. The tempo of these advances is accelerating, promising greater depth and breadth. In light of these extraordinary advances, the need for fast, parallel methods to define gene function becomes ever more important. Collections of genome-wide deletion mutants in yeasts and E. coli have served as workhorses for functional characterization of gene function, but this approach is not scalable, current gene-deletion approaches require each of the thousands of genes that comprise a genome to be deleted and verified. Only after this work is complete can we pursue high-throughput phenotyping. Over the past decade, our laboratory has refined a portfolio of competitive, miniaturized, high-throughput genome-wide assays that can be performed in parallel. This parallelization is possible because of the inclusion of DNA 'tags', or 'barcodes,' into each mutant, with the barcode serving as a proxy for the mutation and one can measure the barcode abundance to assess mutant fitness. In this study, we seek to fill the gap between DNA sequence and barcoded mutant collections. To accomplish this we introduce a combined transposon disruption-barcoding approach that opens up parallel barcode assays to newly sequenced, but poorly characterized microbes. To illustrate this approach we present a new Candida albicans barcoded disruption collection and describe how both microarray-based and next generation sequencing-based platforms can be used to collect 10,000 - 1,000,000 gene-gene and drug-gene interactions in a single experiment.

We have developed comprehensive, unbiased genome-wide screens to understand gene-drug and gene-environment interactions. Methods for screening these mutant collections are presented.

By virtue of advances in next generation sequencing technologies, we have access to new genome sequences almost daily.  The tempo of these advances is ...

Budding Yeast Protein Extraction and Purification for the Study of Function, Interactions, and Post-translational Modifications

Homogenization by bead beating is a fast and efficient way to release DNA, RNA, proteins, and metabolites from budding yeast cells, which are notoriously hard to disrupt. Here we describe the use of a bead mill homogenizer for the extraction of proteins into buffers optimized to maintain the functions, interactions and post-translational modifications of proteins. Logarithmically growing cells expressing the protein of interest are grown in a liquid growth media of choice. The growth media may be supplemented with reagents to induce protein expression from inducible promoters (e.g. galactose), synchronize cell cycle stage (e.g. nocodazole), or inhibit proteasome function (e.g. MG132). Cells are then pelleted and resuspended in a suitable buffer containing protease and/or phosphatase inhibitors and are either processed immediately or frozen in liquid nitrogen for later use. Homogenization is accomplished by six cycles of 20 sec&#160;bead-beating (5.5 m/sec), each followed by one minute incubation on ice. The resulting homogenate is cleared by centrifugation and small particulates can be removed by filtration. The resulting cleared whole cell extract (WCE) is precipitated using 20% TCA for direct analysis of total proteins by SDS-PAGE followed by Western blotting. Extracts are also suitable for affinity purification of specific proteins, the detection of post-translational modifications, or the analysis of co-purifying proteins. As is the case for most protein purification protocols, some enzymes and proteins may require unique conditions or buffer compositions for their purification and others may be unstable or insoluble under the conditions stated. In the latter case, the protocol presented may provide a useful starting point to empirically determine the best bead-beating strategy for protein extraction and purification. We show the extraction and purification of an epitope-tagged SUMO E3 ligase, Siz1, a cell cycle regulated protein that becomes both sumoylated and phosphorylated, as well as a SUMO-targeted ubiquitin ligase subunit, Slx5.

The preparation of high quality yeast cell extracts is a necessary first step in the analysis of individual proteins or entire proteomes. Here we describe a fast, efficient, and reliable homogenization protocol for budding yeast cells that has been optimized to preserve protein functions, interactions, and post-translational modifications.

Homogenization by bead beating is a fast and efficient way to release DNA, RNA, proteins, and metabolites from budding yeast cells, which are notoriously ...

Non-chromatographic Purification of Recombinant Elastin-like Polypeptides and their Fusions with Peptides and Proteins from Escherichia coli

Elastin-like polypeptides are repetitive biopolymers that exhibit a lower critical solution temperature phase transition behavior, existing as soluble unimers below a characteristic transition temperature and aggregating into micron-scale coacervates above their transition temperature. The design of elastin-like polypeptides at the genetic level permits precise control of their sequence and length, which dictates their thermal properties. Elastin-like polypeptides are used in a variety of applications including biosensing, tissue engineering, and drug delivery, where the transition temperature and biopolymer architecture of the ELP can be tuned for the specific application of interest. Furthermore, the lower critical solution temperature phase transition behavior of elastin-like polypeptides allows their purification by their thermal response, such that their selective coacervation and resolubilization allows the removal of both soluble and insoluble contaminants following expression in Escherichia coli. This approach can be used for the purification of elastin-like polypeptides alone or as a purification tool for peptide or protein fusions where recombinant peptides or proteins genetically appended to elastin-like polypeptide tags can be purified without chromatography. This protocol describes the purification of elastin-like polypeptides and their peptide or protein fusions and discusses basic characterization techniques to assess the thermal behavior of pure elastin-like polypeptide products.

Non-chromatographic Purification of Recombinant Elastin-like Polypeptides and their Fusions with Peptides and Proteins from Escherichia coli

Elastin-like polypeptides are stimulus-responsive biopolymers with applications ranging from recombinant protein purification to drug delivery. This protocol describes the purification and characterization of elastin-like polypeptides and their peptide or protein fusions from Escherichia coli using their lower critical solution temperature phase transition behavior as a simple alternative to chromatography.

Elastin-like polypeptides are repetitive biopolymers that exhibit a lower critical solution temperature phase transition behavior, existing as soluble ...