This work was funded by Human Frontier Science Program grant RGP0024.

1. DNA Template Preparation and in vitro Transcription
<ol>
 <li>The gene of interest is cloned under T7 and/or e.g. SP6 transcriptional promoter.</li>
 <li>For in vitro transcription the template DNA is linearized with an appropriate restriction enzyme cutting downstream of the ORF stop codon and/or mRNA 3' end. One needs to verify complete linearization of the plasmid DNA by running the restriction digestion product on agarose gel electrophoresis.</li>
 <li>The linearized plasmid is used for in vitro transcription reaction. Different concentration of template DNA can be tested to identify optimum DNA concentration required for in vitro transcription. Generally, with Ambion's MEGAscript High yield Transcription Kit (Ambion/Life Technologies, Grand Island, NY), 1 &mu;g linearized DNA yields 40-60 &mu;g of mRNA. In vitro transcription is done following manufacturer's instruction (Ambion/Life Technologies, Grand Island, NY).</li>
 <li>Following in vitro transcription the mRNA is purified by lithium chloride precipitation according to manufacturer's instruction (Ambion's MEGAscript High yield Transcription Kit).</li>
 <li>mRNA integrity is further verified by electrophoresis on acrylamide or agarose gels.</li>
</ol>
2. In vitro Cell Free Translation
For in vitro translation using Rabbit Reticulocyte Lysate, RRL (Promega, Madison, WI) follow the steps below:
<ol>
 <li>Prepare 100 &mu;l in vitro translation reaction following manufacturer's instruction. Briefly, in nuclease free water add 2 &mu;l amino acid mixture minus methionine (1 mM), 10 units of RNase Inhibitor (Invitrogen/Life Technologies, Grand Island, NY), 20 &mu;Ci of radioactive [35S]-Methionine (MP Biomedicals, Solon, OH), 70 &mu;l of Rabbit Reticulocyte Lysate (Promega, Madison, WI).</li>
 <li>Incubate the reaction at 30 &deg;C for 5 min to pre warm the translation reaction. Add 2 &mu;g of mRNA to the translation reaction and incubate at 30 &deg;C for 5 min.</li>
 <li>Stop the reaction by placing the translation reaction on ice.</li>
</ol>
3. Isolation of Nascent Polypeptides from in vitro Translation Reaction
<ol>
 <li>To isolate nascent polypeptide bound to ribosomes (polysome), translation reaction is layered on top of 4.5 ml of 30% glycerol in 10 mM Tris-HCl buffer pH 7.6, containing 100 mM KCl, 10 mM MgCI2, and centrifuged at 100,000 X g in a TLA-110 rotor (Beckman Coulter, Inc, Brea, CA) for 1 hr at 4 &deg;C.</li>
 <li>The supernatant is further carefully removed.</li>
 <li>The polysomal pellet containing nascent polypeptides is resuspended in a small volume (10-15 &mu;l) of 1 mM Tris-HCl buffer pH 7.6, containing 0.5 mg/ml ribonuclease A (Invitrogen/Life Technologies, Grand Island, NY), and incubated for 30 min at 37 &deg;C. In order to enhance the hydrolysis of the peptidyl-tRNA ester bond, NaOH is added to a final concentration of 10 mM, and the incubation is continued for additional 30 min.</li>
</ol>
In vitro translation reaction assembled without mRNA and performed under the same conditions (followed by isolation of nascent peptides as has been described) would serve as a major control. Treatment of the translation reaction(s) with puromycin before subjecting the extract to density gradient centrifugation may serve as an additional control.
4. Resolving the Nascent Polypeptide on Tris-tricine SDS PAGE
<ol>
 <li>The isolated nascent polypeptides are resolved and analyzed on Tris- tricine SDS-PAGE. Please note that the amount of the material loaded on the gel will dependent on the efficiency of protein labeling, efficiency on protein translation and many others parameters. The amount of loaded material should be adjusted empirically to allow the best visualization and separation of individual nascent polypeptide chains.</li>
 <li>After electrophoresis gels are fixed, dried using vacuum gel dyer and subjected to autoradiography. The distribution of nascent polypeptides are observed using phosphoimaging.</li>
</ol>
5. Representative Results
Bovine Gamma-B Crystallin was translated in Rabbit Reticulocyte Lysate as well as in E. coli S30 Extract Systems (Promega, Madison, WI) followed by isolation of nascent polypeptide chains. Figure 1 depicts steps involved in isolation of ribosome bound nascent chains. In the present study the aim was to test, if changing the environment of translation i.e. repertoire of tRNAs (known to be substantially different in mammalian (RRL) and prokaryotic (E. coli) systems due to differences in codon bias between the organisms) can alter ribosome movement along mRNA and effect the distribution of translation pause sites. Altered ribosome movement should lead to changes in the distribution of sizes of nascent polypeptides accumulating during translation, as well as their relative intensities. Relative intensities of the bands reflect the duration of the pause. The nascent polypeptides were isolated and resolved on 16.5%T , 6%C Tris-tricine SDS PAGE (Figure 2). Gamma-B Crystallin is a 20 kDa protein. The observation of nascent polypeptides of non-identical lengths and intensities in RRL and E. coli systems indicates that the movement of ribosomes along mRNA in these two systems follows different translation kinetics. For example, we observed a prominent band of 17.7 kDa in E. coli lysate and not in RRL system, suggesting that there is an additional translational pause site in the 3'- end region of mRNA (encoding C-terminal region of Gamma B Crystallin), when it is translated in E. coli system. We note that Gamma-B Crystallin harbors tandem Arg codons (AGG153 and AGA154) that are frequent in mammalian systems, but are known to be extremely rare and slowly translated in E. coli. A novel nascent peptide accumulating in E. coli system (~17.7 kDa Figure 2.2) is likely caused by ribosome pausing at these tandem rare codons. Please note that no bands can be observed in the absence of mRNA (Figure 2.3) and that puromycin treatment removes most of the nascent chains from polysomes (Figure 2.3). Prolonged treatment with puromycin (&gt; 15 min) removes all the nascent chains (data not shown). This confirms that the observed polypeptide products are ribosome associated nascent chains, rather than mRNPs cosedimenting with polysomes.
As mentioned above, codon bias is organism as well as tissue specific. The representative example described here, clearly indicates that changing the environment of translation i.e. repertoire of tRNAs/codon bias can lead to altered movement of ribosome along the mRNA. Evidently, this simple technique can not only allow identification of the translational pause sites along mRNA, but also permits rapid comparison of the translation pause sites between different systems.
<img alt="Figure 1" src="/files/ftp_upload/4026/4026fig1.jpg" /> 
Figure 1. Schematic explaining the steps involved in isolating ribosome bound nascent polypeptides. Bovine Gamma-B Crystallin ORF sequence (528 base pairs) was cloned downstream of T7 promoter in pBSKS+. For in vitro transcription the template DNA was linearized by treating it with EcoRI. Linearized template was used for in vitro transcription. T7 promoter in DNA template is recognized by T7 RNA polymerase that transcribes the downstream Gamma-B Crystallin gene. mRNA is purified using lithium chloride precipitation method. The purified mRNA is used for in vitro translation. Following incubation, translation reaction is layered on top of 30% glycerol solution and centrifuged for 1 hr at 4 &deg;C at 100,000 X g to isolate ribosome bound nascent polypeptides.
<img alt="Figure 2" src="/files/ftp_upload/4026/4026fig2.jpg" /> 
Figure 2. Isolation of Bovine Gamma-B Crystallin nascent polypeptides translated in Rabbit Reticulocyte Lysate (RRL) and E. coli Lysate. 2 &mu;g mRNA was mixed in 100 &mu;l reaction containing RRL or E. coli S30 Extract System (Promega, Madison, WI) according to manufacturer's instruction with 20 &mu;Ci [35S]-Methionine and incubated at 30 &deg;C for 5 min. Following incubation the translation reaction was layered on top of 4.5 ml of 30% glycerol in 10 mM Tris-HCl buffer pH 7.6, containing 100 mM KCl, 10 mM MgCI2, and centrifuged for 1 hr at 4 &deg;C and 100,000 X g in a TLA-110 rotor (Beckman Coulter, Inc, Brea, CA). The isolated polyribosome pellet was resuspended in 20 &mu;l of 1 mM Tris-HCl pH 7.6, containing 0.5 mg/ml ribonuclease A (Invitrogen/Life Technologies, Grand Island, NY) followed by treatment with NaOH (as described in the protocol section). Nascent polypeptides were resolved on 16.5% T, 6% C Tris-Tricine SDS PAGE gel. The gel was dried and exposed for autoradiography. Following exposure the gel was scanned using GE Healthcare's Typhoon Imaging Scanner. Figure 2.1 shows the gel with nascent polypeptides isolated and resolved after translation reactions done in two different systems (RRL and E. coli). Figure 2.2 The gel was analyzed by Image Quant TL, v2005 software and used here as an example to show that the molecular weight and intensity of the nascent polypeptides accumulating in two systems can be easily analyzed and compared. Figure 2.3 shows two sets of controls: nascent polypeptides isolated and resolved on SDS PAGE after translation reactions were assembled without mRNA and/or after the translation reactions were treated with puromycin (5 min, final conc. 1 mM) before the reaction was subjected to centrifugation.

<ol>
	<li>Komar, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+pause+for+thought+along+the+co-translational+folding+pathway.">A pause for thought along the co-translational folding pathway.</a> Trends Biochem. Sci. 34, 16-24 (2009).</li><li>Sharp, P. M., Cowe, E., Higgins, D. G., Shields, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Codon+usage+patterns+in+Escherichia+coli,+Bacillus+subtilis,+Saccharomyces+cerevisiae,+Schizosaccharomyces+pombe,+Drosophila+melanogaster+and+Homo+sapiens;+a+review+of+the+considerable+within-species+diversity.">Codon usage patterns in Escherichia coli, Bacillus subtilis, Saccharomyces cerevisiae, Schizosaccharomyces pombe, Drosophila melanogaster and Homo sapiens; a review of the considerable within-species diversity.</a> Nucleic Acids Res. 16, 8207-8210 (1988).</li><li>Dittmar, K. A., Goodenbour, J. M., Pan, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue-specific+differences+in+human+transfer+RNA+expression.">Tissue-specific differences in human transfer RNA expression.</a> PLoS Genet. 2, e221 (2006).</li><li>Ikemura, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Codon+usage+and+tRNA+content+in+unicellular+and+multicellular+organisms.">Codon usage and tRNA content in unicellular and multicellular organisms.</a> Mol. Biol. Evol. 2, 13-34 (1985).</li><li>Wolin, S. L., Walter, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ribosome+pausing+and+stacking+during+translation+of+a+eukaryotic+mRNA.">Ribosome pausing and stacking during translation of a eukaryotic mRNA.</a> EMBO J. 7, 3559-3569 (1998).</li><li>Krasheninnikov, I. A., Komar, A. A., Adzhubei, I. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonuniform+size+distribution+of+nascent+globin+peptides,+evidence+for+pause+localization+sites,+and+a+cotranslational+protein-folding+model.">Nonuniform size distribution of nascent globin peptides, evidence for pause localization sites, and a cotranslational protein-folding model.</a> J. Protein Chem. 10, 445-454 (1991).</li><li>Komar, A. A., Lesnik, T., Reiss, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synonymous+codon+substitutions+affect+ribosome+traffic+and+protein+folding+during+in+vitro+translation.">Synonymous codon substitutions affect ribosome traffic and protein folding during in vitro translation.</a> FEBS Lett. 462, 387-391 (1999).</li><li>Komar, A. A., Jaenicke, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetics+of+translation+of+&#947;+B+crystallin+and+its+circularly+permutated+variant+in+an+in+vitro+cell-free+system:+possible+relations+to+codon+distribution+and+protein+folding.">Kinetics of translation of &#947; B crystallin and its circularly permutated variant in an in vitro cell-free system: possible relations to codon distribution and protein folding.</a> FEBS Lett. 376, 195-198 (1995).</li><li>Jha, S., Komar, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Birth,+life+and+death+of+nascent+polypeptide+chains.">Birth, life and death of nascent polypeptide chains.</a> Biotechnol. J. 6, 623-640 (2011).</li><li>Thanaraj, T. A., Argos, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ribosome-mediated+translational+pause+and+protein+domain+organization.">Ribosome-mediated translational pause and protein domain organization.</a> Protein Sci. 5, 1594-1612 (1996).</li><li>Kimchi-Sarfaty, C., Oh, J. M., Kim, I. W., Sauna, Z. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+"silent"+polymorphism+in+the+MDR1+gene+changes+substrate+specificity.">A "silent" polymorphism in the MDR1 gene changes substrate specificity.</a> Science. 315, 525-528 (2007).</li><li>Sch&#228;gger, H., von Jagow, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tricine-sodium+dodecyl+sulfate-polyacrylamide+gel+electrophoresis+for+the+separation+of+proteins+in+the+range+from+1+to+100+kDa.">Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis for the separation of proteins in the range from 1 to 100 kDa.</a> Anal. Biochem. 166, 368-379 (1987).</li><li>Shirole, N., Balasubramanian, S., Yanofsky, C., Cruz-Vera, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+Translating+Ribosomes+Containing+Peptidyl-tRNAs+for+Functional+and+Structural+Analyses.">Isolation of Translating Ribosomes Containing Peptidyl-tRNAs for Functional and Structural Analyses.</a> J. Vis. Exp. (48), e2498 (2011).</li><li>Ingolia, N. T., Ghaemmaghami, S., Newman, J. R. S., Weissman, J. S. <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+analysis+in+vivo+of+translation+with+nucleotide+resolution+using+ribosome+profiling.">Genome-wide analysis in vivo of translation with nucleotide resolution using ribosome profiling.</a> Science. 324, 218-223 (2009).</li></ol>

No conflicts of interest declared.

For reproducible results, quality and concentration of the components used for in vitro transcription and translation reactions are critical. In the current study we have used commercially available kits and extracts that provide highly reproducible data, if handled carefully. However, translation-competent extracts can be prepared from the cell of one's choice, if needed. Quality of mRNA can affect the translation, so it is of utmost importance to test the integrity of mRNAs before using it during in vitro<...

<table border="1">
	<tbody>
		<tr>
			<td>Name of reagent/ Kit</td>
			<td>Company</td>
			<td>Catalogue number</td>
		</tr>
		<tr>
			<td>MEGAscript T7 High yield Transcription Kit</td>
			<td>Ambion</td>
			<td>AM1333</td>
		</tr>
		<tr>
			<td>Ribonuclease Inhibitor</td>
			<td>Invitrogen</td>
			<td>15518012</td>
		</tr>
		<tr>
			<td>Trans [35S]-Label</td>
			<td>MP Biomedicals</td>
			<td>0151006</td>
		</tr>
		<tr>
			<td>Ribonuclease-A</td>
			<td>Invitrogen</td>
			<td>12091</td>
		</tr>
		<tr>
			<td>Rabbit Reticulocyte Lysate System, Nuclease Treated</td>
			<td>Promega</td>
			<td>L4960</td>
		</tr>
		<tr>
			<td>E. coli S30 Extract System for Linear Templates</td>
			<td>Promega</td>
			<td>L1030</td>
		</tr>
		<tr>
			<td>Centrifugation</td>
			<td>Beckman Coulter</td>
			<td>Optima TLX Ultracentrifuge</td>
		</tr>
		<tr>
			<td>Storage phosphor autoradiography</td>
			<td>GE Healthcare</td>
			<td>Typhoon 9410 variable mode imager</td>
		</tr>
		<tr>
			<td>Software for nascent polypeptide analysis</td>
			<td>GE Healthcare</td>
			<td>Image Quant TL, v2005</td>
		</tr>
	</tbody>
</table>

isolation of ribosome bound nascent polypeptides in vitro to identify translational pause sites along mrna

The rate of translational elongation is non-uniform. mRNA secondary structure, codon usage and mRNA associated proteins may alter ribosome movement on the messagefor review see 1. However, it's now widely accepted that synonymous codon usage is the primary cause of non-uniform translational elongation rates1. Synonymous codons are not used with identical frequency. A bias exists in the use of synonymous codons with some codons used more frequently than others2. Codon bias is organism as well as tissue specific2,3. Moreover, frequency of codon usage is directly proportional to the concentrations of cognate tRNAs4. Thus, a frequently used codon will have higher multitude of corresponding tRNAs, which further implies that a frequent codon will be translated faster than an infrequent one. Thus, regions on mRNA enriched in rare codons (potential pause sites) will as a rule slow down ribosome movement on the message and cause accumulation of nascent peptides of the respective sizes5-8. These pause sites can have functional impact on the protein expression, mRNA stability and protein foldingfor review see 9. Indeed, it was shown that alleviation of such pause sites can alter ribosome movement on mRNA and subsequently may affect the efficiency of co-translational (in vivo) protein folding1,7,10,11. To understand the process of protein folding in vivo, in the cell, that is ultimately coupled to the process of protein synthesis it is essential to gain comprehensive insights into the impact of codon usage/tRNA content on the movement of ribosomes along mRNA during translational elongation.
Here we describe a simple technique that can be used to locate major translation pause sites for a given mRNA translated in various cell-free systems6-8. This procedure is based on isolation of nascent polypeptides accumulating on ribosomes during in vitro translation of a target mRNA. The rationale is that at low-frequency codons, the increase in the residence time of the ribosomes results in increased amounts of nascent peptides of the corresponding sizes. In vitro transcribed mRNA is used for in vitro translational reactions in the presence of radioactively labeled amino acids to allow the detection of the nascent chains. In order to isolate ribosome bound nascent polypeptide complexes the translation reaction is layered on top of 30% glycerol solution followed by centrifugation. Nascent polypeptides in polysomal pellet are further treated with ribonuclease A and resolved by SDS PAGE. This technique can be potentially used for any protein and allows analysis of ribosome movement along mRNA and the detection of the major pause sites. Additionally, this protocol can be adapted to study factors and conditions that can alter ribosome movement and thus potentially can also alter the function/conformation of the protein.

Watch this Scientific Journal Video about Isolation of Ribosome Bound Nascent Polypeptides in vitro to Identify Translational Pause Sites Along mRNA at JoVE.com

Isolation of Ribosome Bound Nascent Polypeptides in vitro to Identify Translational Pause Sites Along mRNA

A technique to identify translational pause sites on mRNA is described. This procedure is based on isolation of nascent polypeptides accumulating on ribosomes during in vitro translation of a target mRNA, followed by the size analysis of the nascent chains using a denaturing gel electrophoresis.

Isolation of Ribosome Bound Nascent Polypeptides in vitro to Identify Translational Pause Sites Along mRNA

The rate of translational elongation is non-uniform. mRNA secondary structure, codon usage and mRNA associated proteins may alter ribosome movement on the ...

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16.2K Views.  Cleveland State University. טכניקה לזהות אתרים על הפסקה של תרגום ה-mRNA מתואר. הליך זה מבוסס על בידוד של פוליפפטידים המתהווה המצטברים על הריבוזומים במהלך בתרגום חוץ גופית של mRNA המטרה, ואחריו ניתוח בגודל של רשתות המתהווה באמצעות ג'ל אלקטרופורזה denaturing.

Video: Isolation of Ribosome Bound Nascent Polypeptides in vitro to Identify Translational Pause Sites Along mRNA

PAR-CliP - A Method to Identify Transcriptome-wide the Binding Sites of RNA Binding Proteins

RNA transcripts are subjected to post-transcriptional gene regulation by interacting with hundreds of RNA-binding proteins (RBPs) and microRNA-containing ribonucleoprotein complexes (miRNPs) that are often expressed in a cell-type dependently. To understand how the interplay of these RNA-binding factors affects the regulation of individual transcripts, high resolution maps of in vivo protein-RNA interactions are necessary1.
A combination of genetic, biochemical and computational approaches are typically applied to identify RNA-RBP or RNA-RNP interactions. Microarray profiling of RNAs associated with immunopurified RBPs (RIP-Chip)2 defines targets at a transcriptome level, but its application is limited to the characterization of kinetically stable interactions and only in rare cases3,4 allows to identify the RBP recognition element (RRE) within the long target RNA. More direct RBP target site information is obtained by combining in vivo UV crosslinking5,6 with immunoprecipitation7-9 followed by the isolation of crosslinked RNA segments and cDNA sequencing (CLIP)10. CLIP was used to identify targets of a number of RBPs11-17. However, CLIP is limited by the low efficiency of UV 254 nm RNA-protein crosslinking, and the location of the crosslink is not readily identifiable within the sequenced crosslinked fragments, making it difficult to separate UV-crosslinked target RNA segments from background non-crosslinked RNA fragments also present in the sample.
We developed a powerful cell-based crosslinking approach to determine at high resolution and transcriptome-wide the binding sites of cellular RBPs and miRNPs that we term PAR-CliP (Photoactivatable-Ribonucleoside-Enhanced Crosslinking and Immunoprecipitation) (see Fig. 1A for an outline of the method). The method relies on the incorporation of photoreactive ribonucleoside analogs, such as 4-thiouridine (4-SU) and 6-thioguanosine (6-SG) into nascent RNA transcripts by living cells. Irradiation of the cells by UV light of 365 nm induces efficient crosslinking of photoreactive nucleoside-labeled cellular RNAs to interacting RBPs. Immunoprecipitation of the RBP of interest is followed by isolation of the crosslinked and coimmunoprecipitated RNA. The isolated RNA is converted into a cDNA library and deep sequenced using Solexa technology. One characteristic feature of cDNA libraries prepared by PAR-CliP is that the precise position of crosslinking can be identified by mutations residing in the sequenced cDNA. When using 4-SU, crosslinked sequences thymidine to cytidine transition, whereas using 6-SG results in guanosine to adenosine mutations. The presence of the mutations in crosslinked sequences makes it possible to separate them from the background of sequences derived from abundant cellular RNAs.
Application of the method to a number of diverse RNA binding proteins was reported in Hafner et al.18

RNA transcripts are subject to extensive posttranscriptional regulation that is mediated by a multitude of trans-acting RNA-binding proteins (RBPs). Here we present a generalizable method to identify precisely and on a transcriptome-wide scale the RNA binding sites of RBPs.

RNA transcripts are subjected to post-transcriptional gene regulation by interacting with hundreds of RNA-binding proteins (RBPs) and microRNA-containing ...

Isolation and In vitro Activation of Caenorhabditis elegans Sperm

Males and hermaphrodites are the two naturally found sexual forms in the nematode C. elegans. The amoeboid sperm are produced by both males and hermaphrodites. In the earlier phase of gametogenesis, the germ cells of hermaphrodites differentiate into limited number of sperm - around 300 - and are stored in a small 'bag' called the spermatheca. Later on, hermaphrodites continually produce oocytes1. In contrast, males produce exclusively sperm throughout their adulthood. The males produce so much sperm that it accounts for &gt;50% of the total cells in a typical adult worm2. Therefore, isolating sperm from males is easier than from that of hermaphrodites.
Only a small proportion of males are naturally generated due to spontaneous non-disjunction of X chromosome3. Crossing hermaphrodites with males or more conveniently, the introduction of mutations to give rise to Him (High Incidence of Males) phenotype are some of strategies through which one can enrich the male population3.
Males can be easily distinguished from hermaphrodites by observing the tail morphology4. Hermaphrodite's tail is pointed, whereas male tail is rounded with mating structures.
Cutting the tail releases vast number of spermatids stored inside the male reproductive tract. Dissection is performed under a stereo microscope using 27 gauge needles. Since spermatids are not physically connected with any other cells, hydraulic pressure expels internal contents of male body, including spermatids2.
Males are directly dissected on a small drop of 'Sperm Medium'. Spermatids are sensitive to alteration in the pH. Hence, HEPES, a compound with good buffering capacity is used in sperm media. Glucose and other salts present in sperm media help maintain osmotic pressure to maintain the integrity of sperm.
Post-meiotic differentiation of spermatids into spermatozoa is termed spermiogenesis or sperm activation. Shakes5, and Nelson6 previously showed that round spermatids can be induced to differentiate into spermatozoa by adding various activating compounds including Pronase E. Here we demonstrate in vitro spermiogenesis of C. elegans spermatids using Pronase E.
Successful spermiogenesis is pre-requisite for fertility and hence the mutants defective in spermiogenesis are sterile. Hitherto several mutants have been shown to be defective specifically in spermiogenesis process7. Abnormality found during in vitro activation of novel Spe (Spermatogenesis defective) mutants would help us discover additional players participating in this event.

Isolation and In vitro Activation of Caenorhabditis elegans Sperm

A protocol for isolating and activating spermatids from male C. elegans is described here. Cutting the posterior end of male releases spermatids. The spermatids can be activated by addition of protease.

Males and hermaphrodites are the two naturally found sexual forms in the nematode C. elegans. The amoeboid sperm are produced by both males and ...

Using SCOPE to Identify Potential Regulatory Motifs in Coregulated Genes

SCOPE is an ensemble motif finder that uses three component algorithms in parallel to identify potential regulatory motifs by over-representation and motif position preference1. Each component algorithm is optimized to find a different kind of motif. By taking the best of these three approaches, SCOPE performs better than any single algorithm, even in the presence of noisy data1. In this article, we utilize a web version of SCOPE2 to examine genes that are involved in telomere maintenance. SCOPE has been incorporated into at least two other motif finding programs3,4 and has been used in other studies5-8. 
The three algorithms that comprise SCOPE are BEAM9, which finds non-degenerate motifs (ACCGGT), PRISM10, which finds degenerate motifs (ASCGWT), and SPACER11, which finds longer bipartite motifs (ACCnnnnnnnnGGT). These three algorithms have been optimized to find their corresponding type of motif. Together, they allow SCOPE to perform extremely well.
Once a gene set has been analyzed and candidate motifs identified, SCOPE can look for other genes that contain the motif which, when added to the original set, will improve the motif score. This can occur through over-representation or motif position preference. Working with partial gene sets that have biologically verified transcription factor binding sites, SCOPE was able to identify most of the rest of the genes also regulated by the given transcription factor.
Output from SCOPE shows candidate motifs, their significance, and other information both as a table and as a graphical motif map. FAQs and video tutorials are available at the SCOPE web site which also includes a "Sample Search" button that allows the user to perform a trial run. 
Scope has a very friendly user interface that enables novice users to access the algorithm's full power without having to become an expert in the bioinformatics of motif finding. As input, SCOPE can take a list of genes, or FASTA sequences. These can be entered in browser text fields, or read from a file. The output from SCOPE contains a list of all identified motifs with their scores, number of occurrences, fraction of genes containing the motif, and the algorithm used to identify the motif. For each motif, result details include a consensus representation of the motif, a sequence logo, a position weight matrix, and a list of instances for every motif occurrence (with exact positions and "strand" indicated). Results are returned in a browser window and also optionally by email. Previous papers describe the SCOPE algorithms in detail1,2,9-11.

A straight-forward and robust method to identify potential regulatory motifs in co-regulated genes is presented. SCOPE does not require any user parameters and returns motifs that represent excellent candidates for regulatory signals. The identification of such regulatory signals helps to understand the underlying biology.

SCOPE is an ensemble motif finder that uses three component algorithms in parallel to identify potential regulatory motifs by over-representation and ...

In vitro Transcription and Capping of Gaussia Luciferase mRNA Followed by HeLa Cell Transfection

In vitro transcription is the synthesis of RNA transcripts by RNA polymerase from a linear DNA template containing the corresponding promoter sequence (T7, T3, SP6) and the gene to be transcribed (Figure 1A). A typical transcription reaction consists of the template DNA, RNA polymerase, ribonucleotide triphosphates, RNase inhibitor and buffer containing Mg2+ ions.
Large amounts of high quality RNA are often required for a variety of applications. Use of in vitro transcription has been reported for RNA structure and function studies such as splicing1, RNAi experiments in mammalian cells2, antisense RNA amplification by the "Eberwine method"3, microarray analysis4 and for RNA vaccine studies5. The technique can also be used for producing radiolabeled and dye labeled probes6. Warren, et al. recently reported reprogramming of human cells by transfection with in vitro transcribed capped RNA7. The T7 High Yield RNA Synthesis Kit from New England Biolabs has been designed to synthesize up to 180 &mu;g RNA per 20 &mu;l reaction. RNA of length up to 10kb has been successfully transcribed using this kit. Linearized plasmid DNA, PCR products and synthetic DNA oligonucleotides can be used as templates for transcription as long as they have the T7 promoter sequence upstream of the gene to be transcribed.
Addition of a 5' end cap structure to the RNA is an important process in eukaryotes. It is essential for RNA stability8, efficient translation9, nuclear transport10 and splicing11. The process involves addition of a 7-methylguanosine cap at the 5' triphosphate end of the RNA. RNA capping can be carried out post-transcriptionally using capping enzymes or co-transcriptionally using cap analogs. In the enzymatic method, the mRNA is capped using the Vaccinia virus capping enzyme12,13. The enzyme adds on a 7-methylguanosine cap at the 5' end of the RNA using GTP and S-adenosyl methionine as donors (cap 0 structure). Both methods yield functionally active capped RNA suitable for transfection or other applications14 such as generating viral genomic RNA for reverse-genetic systems15 and crystallographic studies of cap binding proteins such as eIF4E16.
In the method described below, the T7 High Yield RNA Synthesis Kit from NEB is used to synthesize capped and uncapped RNA transcripts of Gaussia luciferase (GLuc) and Cypridina luciferase (CLuc). A portion of the uncapped GLuc RNA is capped using the Vaccinia Capping System (NEB). A linearized plasmid containing the GLuc or CLuc gene and T7 promoter is used as the template DNA. The transcribed RNA is transfected into HeLa cells and cell culture supernatants are assayed for luciferase activity. Capped CLuc RNA is used as the internal control to normalize GLuc expression.

In vitro Transcription and Capping of Gaussia Luciferase mRNA Followed by HeLa Cell Transfection

This method describes high yield in vitro synthesis of both capped and uncapped mRNA from a linearized plasmid containing the Gaussia luciferase (GLuc) gene. The RNA is purified and a fraction of the uncapped RNA is enzymatically capped using the Vaccinia virus capping enzyme. In the final step, the mRNA is transfected into HeLa cells and cell culture supernatants are assayed for luciferase activity.

In vitro transcription is the synthesis of RNA transcripts by RNA polymerase from a linear DNA template containing the corresponding promoter sequence ...

Using SecM Arrest Sequence as a Tool to Isolate Ribosome Bound Polypeptides

Extensive research has provided ample evidences suggesting that protein folding in the cell is a co-translational process1-5. However, the exact pathway that polypeptide chain follows during co-translational folding to achieve its functional form is still an enigma. In order to understand this process and to determine the exact conformation of the co-translational folding intermediates, it is essential to develop techniques that allow the isolation of RNCs carrying nascent chains of predetermined sizes to allow their further structural analysis.
SecM (secretion monitor) is a 170 amino acid E. coli protein that regulates expression of the downstream SecA (secretion driving) ATPase in the secM-secA operon6. Nakatogawa and Ito originally found that a 17 amino acid long sequence (150-FSTPVWISQAQGIRAGP-166) in the C-terminal region of the SecM protein is sufficient and necessary to cause stalling of SecM elongation at Gly165, thereby producing peptidyl-glycyl-tRNA stably bound to the ribosomal P-site7-9. More importantly, it was found that this 17 amino acid long sequence can be fused to the C-terminus of virtually any full-length and/or truncated protein thus allowing the production of RNCs carrying nascent chains of predetermined sizes7. Thus, when fused or inserted into the target protein, SecM stalling sequence produces arrest of the polypeptide chain elongation and generates stable RNCs both in vivo in E. coli cells and in vitro in a cell-free system. Sucrose gradient centrifugation is further utilized to isolate RNCs.
The isolated RNCs can be used to analyze structural and functional features of the co-translational folding intermediates. Recently, this technique has been successfully used to gain insights into the structure of several ribosome bound nascent chains10,11. Here we describe the isolation of bovine Gamma-B Crystallin RNCs fused to SecM and generated in an in vitro translation system.

We describe here a technique that is now routinely used to isolate stably bound ribosome nascent chain complexes (RNCs). This technique takes advantage of the discovery that a 17 amino acid long SecM "arrest sequence" can halt translation elongation in a prokaryotic (E. coli) system, when inserted into (or fused to the C-terminus) of virtually any protein.

Extensive research has provided ample evidences suggesting that protein folding in the cell is a co-translational process1-5. However, the exact pathway ...

In Vitro Synthesis of Modified mRNA for Induction of Protein Expression in Human Cells

The exogenous delivery of coding synthetic messenger RNA (mRNA) for induction of protein synthesis in desired cells has enormous potential in the fields of regenerative medicine, basic cell biology, treatment of diseases, and reprogramming of cells. Here, we describe a step by step protocol for generation of modified mRNA with reduced immune activation potential and increased stability, quality control of produced mRNA, transfection of cells with mRNA and verification of the induced protein expression by flow cytometry. Up to 3 days after a single transfection with eGFP mRNA, the transfected HEK293 cells produce eGFP. In this video article, the synthesis of eGFP mRNA is described as an example. However, the procedure can be applied for production of other desired mRNA. Using the synthetic modified mRNA, cells can be induced to transiently express the desired proteins, which they normally would not express.

In Vitro Synthesis of Modified mRNA for Induction of Protein Expression in Human Cells

In this video article, we describe the in vitro synthesis of modified mRNA for induction of protein expression in cells.

The exogenous delivery of coding synthetic messenger RNA (mRNA) for induction of protein synthesis in desired cells has enormous potential in the fields ...

Measuring Oxidative Stress Resistance of Caenorhabditis elegans in 96-well Microtiter Plates

Oxidative stress, which is the result of an imbalance between production and detoxification of reactive oxygen species, is a major contributor to chronic human disorders, including cardiovascular and neurodegenerative diseases, diabetes, aging, and cancer. Therefore, it is important to study oxidative stress not only in cell systems but also using whole organisms. C. elegans is an attractive model organism to study the genetics of oxidative stress signal transduction pathways, which are highly evolutionarily conserved.
Here, we provide a protocol to measure oxidative stress resistance in C. elegans in liquid. Briefly, ROS-inducing reagents such as paraquat (PQ) and H2O2 are dissolved in M9 buffer, and solutions are aliquoted in the wells of a 96 well microtiter plate. Synchronized L4/young adult C. elegans animals are transferred to the wells (5-8 animals/well) and survival is measured every hour until most worms are dead. When performing an oxidative stress resistance assay using a low concentration of stressors in plates, aging might influence the behavior of animals upon oxidative stress, which could lead to an incorrect interpretation of the data. However, in the assay described herein, this problem is unlikely to occur since only L4/young adult animals are being used. Moreover, this protocol is inexpensive and results are obtained in one day, which renders this technique attractive for genetic screens. Overall, this will help to understand oxidative stress signal transduction pathways, which could be translated into better characterization of oxidative stress-associated human disorders.

Measuring Oxidative Stress Resistance of Caenorhabditis elegans in 96-well Microtiter Plates

C. elegans is an attractive model organism to study signal transduction pathways involved in oxidative stress resistance. Here we provide a protocol to measure oxidative stress resistance of C. elegans animals in liquid phase, using several oxidizing agents in 96 well plates.

Oxidative stress, which is the result of an imbalance between production and detoxification of reactive oxygen species, is a major contributor to chronic ...

Examination of Proteins Bound to Nascent DNA in Mammalian Cells Using  BrdU-ChIP-Slot-Western Technique

Histone deacetylases 1 and 2 (HDAC1,2) localize to the sites of DNA replication. In the previous study, using a selective inhibitor and a genetic knockdown system, we showed novel functions for HDAC1,2 in replication fork progression and nascent chromatin maintenance in mammalian cells. Additionally, we used a BrdU-ChIP-Slot-Western technique that combines chromatin immunoprecipitation (ChIP) of bromo-deoxyuridine (BrdU)-labeled DNA with slot blot and Western analyses to quantitatively measure proteins or histone modification associated with nascent DNA.
Actively dividing cells were treated with HDAC1,2 selective inhibitor or transfected with siRNAs against Hdac1 and Hdac2 and then newly synthesized DNA was labeled with the thymidine analog bromodeoxyuridine (BrdU). The BrdU labeling was done at a time point when there was no significant cell cycle arrest or apoptosis due to the loss of HDAC1,2 functions. Following labeling of cells with BrdU, chromatin immunoprecipitation (ChIP) of histone acetylation marks or the chromatin-remodeler was performed with specific antibodies. BrdU-labeled input DNA and the immunoprecipitated (or ChIPed) DNA was then spotted onto a membrane using the slot blot technique and immobilized using UV. The amount of nascent DNA in each slot was then quantitatively assessed using Western analysis with an anti-BrdU antibody. The effect of loss of HDAC1,2 functions on the levels of newly synthesized DNA-associated histone acetylation marks and chromatin remodeler was then determined by normalizing the BrdU-ChIP signal obtained from the treated samples to the control samples.

In this protocol, we describe a novel BrdU-ChIP-Slot-Western technique to examine proteins and histone modifications associated with newly synthesized or nascent DNA.

Histone deacetylases 1 and 2 (HDAC1,2) localize to the sites of DNA replication. In the previous study, using a selective inhibitor and a genetic ...

A Protocol for Using Gene Set Enrichment Analysis to Identify the Appropriate Animal Model for Translational Research

Recent studies that compared transcriptomic datasets of human diseases with datasets from mouse models using traditional gene-to-gene comparison techniques resulted in contradictory conclusions regarding the relevance of animal models for translational research. A major reason for the discrepancies between different gene expression analyses is the arbitrary filtering of differentially expressed genes. Furthermore, the comparison of single genes between different species and platforms often is limited by technical variance, leading to misinterpretation of the con/discordance between data from human and animal models. Thus, standardized approaches for systematic data analysis are needed. To overcome subjective gene filtering and ineffective gene-to-gene comparisons, we recently demonstrated that gene set enrichment analysis (GSEA) has the potential to avoid these problems. Therefore, we developed a standardized protocol for the use of GSEA to distinguish between appropriate and inappropriate animal models for translational research. This protocol is not suitable to predict how to design new model systems a-priori, as it requires existing experimental omics data. However, the protocol describes how to interpret existing data in a standardized manner in order to select the most suitable animal model, thus avoiding unnecessary animal experiments and misleading translational studies.

We provide a standardized protocol for the use of gene set enrichment analysis of transcriptomic data to identify an ideal mouse model for translational research. 
This protocol can be used with DNA microarray and RNA sequencing data and can further be extended to other omics data if data are available.

Recent studies that compared transcriptomic datasets of human diseases with datasets from mouse models using traditional gene-to-gene comparison ...

In Vitro SUMOylation Assay to Study SUMO E3 Ligase Activity

Small ubiquitin-like modifier (SUMO) modification is an important post-translational modification (PTM) that mediates signal transduction primarily through modulating protein-protein interactions. Similar to ubiquitin modification, SUMOylation is directed by a sequential enzyme cascade including E1-activating enzyme (SAE1/SAE2), E2-conjugation enzyme (Ubc9), and E3-ligase (i.e., PIAS family, RanBP2, and Pc2). However, different from ubiquitination, an E3 ligase is non-essential for the reaction but does provide precision and efficacy for SUMO conjugation. Proteins modified by SUMOylation can be identified by in vivo assay via immunoprecipitation with substrate-specific antibodies and immunoblotting with SUMO-specific antibodies. However, the demonstration of protein SUMO E3 ligase activity requires in vitro reconstitution of SUMOylation assays using purified enzymes, substrate, and SUMO proteins. Since in the in vitro reactions, usually SAE1/SAE2 and Ubc9, alone are sufficient for SUMO conjugation, enhancement of SUMOylation by a putative E3 ligase is not always easy to detect. Here, we describe a modified in vitro SUMOylation protocol that consistently identifies SUMO modification using an in vitro reconstituted system. A step-by-step protocol to purify catalytically active K-bZIP, a viral SUMO-2/3 E3 ligase, is also presented. The SUMOylation activities of the purified K-bZIP are shown on p53, a well-known target of SUMO. This protocol can not only be employed for elucidating novel SUMO E3 ligases, but also for revealing their SUMO paralog specificity.

In Vitro SUMOylation Assay to Study SUMO E3 Ligase Activity

Unlike ubiquitin ligases, few E3 SUMO ligases have been identified. This modified in vitro SUMOylation protocol is able to identify novel SUMO E3 ligases by an in vitro reconstitution assay.

Small ubiquitin-like modifier (SUMO) modification is an important post-translational modification (PTM) that mediates signal transduction primarily ...