The authors thank Marit Warrer for excellent technical assistance. This work was supported by the Danish Council for Independent Research | Natural Sciences [1323-00343B] and the Danish National Research Foundation [DNRF120].

1. Preparation of bacterial cultures.
<ol>
	<li>Grow all cultures in Erlenmeyer flasks with a culture/flask volume ratio of at most 1/6. In a typical experimental setup, grow the cultures at 37.0 &#176;C and shaking at 160 rpm in morpholinepropanesulfonic acid (MOPS) minimal medium18 supplemented with the preferred carbon source, for example 0.2% glucose, for at least 10 consecutive generations before RNA harvest.</li>
	<li>The day before RNA harvest, dilute an outgrown culture of the desired st...

<ol>
	<li>Varshney, U., Lee, C. -. P., RajBhandary, U. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+analysis+of+aminoacylation+levels+of+tRNAs+in+vivo.+Application+to+studying+recognition+of+Escherichia+coli+initiator+tRNA+mutants+by+glutaminyl-tRNA+synthetase.">Direct analysis of aminoacylation levels of tRNAs in vivo. Application to studying recognition of Escherichia coli initiator tRNA mutants by glutaminyl-tRNA synthetase.</a> J Biol Chem. 266 (36), 24712-24718 (1991).</li><li>Sorensen, 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=Charging+levels+of+four+tRNA+species+in+Escherichia+coli+Rel(+)+and+Rel(-)+strains+during+amino+acid+starvation:+a+simple+model+for+the+effect+of+ppGpp+on+translational+accuracy.">Charging levels of four tRNA species in Escherichia coli Rel(+) and Rel(-) strains during amino acid starvation: a simple model for the effect of ppGpp on translational accuracy.</a> J Mol Biol. 307 (3), 785-798 (2001).</li><li>Kr&#252;ger, M. K., S&#248;rensen, 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=Aminoacylation+of+hypomodified+tRNAGlu+in+vivo.">Aminoacylation of hypomodified tRNAGlu in vivo.</a> J. Mol. Biol. 284 (3), 609-620 (1998).</li><li>Svenningsen, S. L., Kongstad, M., Stenum, T. S., Mu&#241;oz-G&#243;mez, A. J., S&#248;rensen, 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=Transfer+RNA+is+highly+unstable+during+early+amino+acid+starvation+in+Escherichia+coli.">Transfer RNA is highly unstable during early amino acid starvation in Escherichia coli.</a> Nucleic Acids Res. 45 (2), 793-804 (2017).</li><li>Enriquez, J. A., Attardi, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+for+aminoacylation-induced+conformational+changes+in+human+mitochondrial+tRNAs.">Evidence for aminoacylation-induced conformational changes in human mitochondrial tRNAs.</a> Proc Natl Acad Sci U S A. 93 (16), 8300-8305 (1996).</li><li>Parker, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Errors+and+alternatives+in+reading+the+universal+genetic+code.">Errors and alternatives in reading the universal genetic code.</a> Microbiol Rev. 53 (3), 273-298 (1989).</li><li>Traxler, M. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+global,+ppGpp-mediated+stringent+response+to+amino+acid+starvation+in+Escherichia+coli.">The global, ppGpp-mediated stringent response to amino acid starvation in Escherichia coli.</a> Mol Microbiol. 68 (5), 1128-1148 (2008).</li><li>Zhong, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transfer+RNAs+Mediate+the+Rapid+Adaptation+of+Escherichia+coli+to+Oxidative+Stress.">Transfer RNAs Mediate the Rapid Adaptation of Escherichia coli to Oxidative Stress.</a> PLoS Genet. 11 (6), e1005302 (2015).</li><li>Kane, J. F. <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+rare+codon+clusters+on+high-level+expression+of+heterologous+proteins+in+Escherichia+coli.">Effects of rare codon clusters on high-level expression of heterologous proteins in Escherichia coli.</a> Curr Opin Biotechnol. 6 (5), 494-500 (1995).</li><li>Baca, A. M., Hol, W. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Overcoming+codon+bias:+a+method+for+high-level+overexpression+of+Plasmodium+and+other+AT-rich+parasite+genes+in+Escherichia+coli.">Overcoming codon bias: a method for high-level overexpression of Plasmodium and other AT-rich parasite genes in Escherichia coli.</a> Int J Parasitol. 30 (2), 113-118 (2000).</li><li>Li, S., Pelka, H., Schulman, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+anticodon+and+discriminator+base+are+important+for+aminoacylation+of+Escherichia+coli+tRNA+(Asn).">The anticodon and discriminator base are important for aminoacylation of Escherichia coli tRNA (Asn).</a> J Biol Chem. 268 (24), 18335-18339 (1993).</li><li>Rizzino, A. A., Freundlich, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Estimation+of+in+vivo+aminoacylation+by+periodate+oxidation:+tRNA+alterations+and+iodate+inhibition.">Estimation of in vivo aminoacylation by periodate oxidation: tRNA alterations and iodate inhibition.</a> Anal Biochem. 66 (2), 446-449 (1975).</li><li>Dittmar, K. A., Sorensen, M. A., Elf, J., Ehrenberg, 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=Selective+charging+of+tRNA+isoacceptors+induced+by+amino-acid+starvation.">Selective charging of tRNA isoacceptors induced by amino-acid starvation.</a> EMBO Rep. 6 (2), 151-157 (2005).</li><li>Zhou, K., 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=Novel+reference+genes+for+quantifying+transcriptional+responses+of+Escherichia+coli+to+protein+overexpression+by+quantitative+PCR.">Novel reference genes for quantifying transcriptional responses of Escherichia coli to protein overexpression by quantitative PCR.</a> BMC Mol Biol. 12 (1), 18 (2011).</li><li>Jacobson, A., Gillespie, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metabolic+events+occurring+during+recovery+from+prolonged+glucose+starvation+in+Escherichia+coli.">Metabolic events occurring during recovery from prolonged glucose starvation in Escherichia coli.</a> J Bacteriol. 95 (3), 1030-1039 (1968).</li><li>McCarthy, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effects+of+magnesium+starvation+on+the+ribosome+content+of+Escherichia+coli.">The effects of magnesium starvation on the ribosome content of Escherichia coli.</a> Biochim Biophys Acta (BBA)-Specialized Section on Nucleic Acids and Related Subjects. 55 (6), 880-889 (1962).</li><li>Zundel, M. A., Basturea, G. N., Deutscher, M. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Initiation+of+ribosome+degradation+during+starvation+in+Escherichia+coli.">Initiation of ribosome degradation during starvation in Escherichia coli.</a> Rna. 15 (5), 977-983 (2009).</li><li>Piir, K., Paier, A., Liiv, A., Tenson, T., Maivali, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ribosome+degradation+in+growing+bacteria.">Ribosome degradation in growing bacteria.</a> EMBO Rep. 12 (5), 458-462 (2011).</li><li>Schaechter, M., Maaloe, O., Kjeldgaard, N. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dependency+on+medium+and+temperature+of+cell+size+and+chemical+composition+during+balanced+grown+of+Salmonella+typhimurium.">Dependency on medium and temperature of cell size and chemical composition during balanced grown of Salmonella typhimurium.</a> J Gen Microbiol. 19 (3), 592-606 (1958).</li><li>Neidhardt, F. C., Bloch, P. L., Smith, D. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Culture+medium+for+enterobacteria.">Culture medium for enterobacteria.</a> J Bacteriol. 119 (3), 736-747 (1974).</li><li>Sambrook, J., Fritsch, E. F., Maniatis, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Molecular cloning: a laboratory manual. , (1989).</li><li>Sorensen, M. A., Jensen, K. F., Pedersen, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+concentrations+of+ppGpp+decrease+the+RNA+chain+growth+rate.+Implications+for+protein+synthesis+and+translational+fidelity+during+amino+acid+starvation+in+Escherichia+coli.">High concentrations of ppGpp decrease the RNA chain growth rate. Implications for protein synthesis and translational fidelity during amino acid starvation in Escherichia coli.</a> J Mol Biol. 236 (2), 441-454 (1994).</li><li>Tian, C., 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=Rapid+Curtailing+of+the+Stringent+Response+by+Toxin-Antitoxin+Module-Encoded+mRNases.">Rapid Curtailing of the Stringent Response by Toxin-Antitoxin Module-Encoded mRNases.</a> J Bacteriol. 198 (14), 1918-1926 (2016).</li></ol>

This protocol describes how to simultaneously measure the charging level of specific E. coli tRNAs and compare the relative levels of the tRNAs in different samples. The critical points of the protocol are 1) to handle the samples in such a way that the cellular tRNA charging levels are retained, 2) to normalize tRNA quantities in such a way that relative tRNA levels in different samples can be reliably compared, and 3) to ensure the specificity of the selected probes for the tRNAs of interest. These points are ...

In the following, we present a method for quantifying specific tRNAs and measuring their charging levels by Northern blotting. The method is based on a technique first developed by Varshney et al.1. By harvesting cells into trichloroacetic acid (TCA) and keeping the samples at 0 &#176;C throughout the RNA purification, the ester bond between the tRNA and the amino acid is conserved2,3,4. Aminoacylated tRNAs can be distinguished from their nonacylated counterparts by gel electrophoresis and Northern blotting, due to a decreased mobility of the aminoacylated tRNA in the gel, caused by the covalently bound amino acid5. Additionally, we present a protocol for normalizing tRNA quantities by addition of spike-in cells overexpressing the rarely used tRNAselC 4.
tRNAs are some of the most abundant molecules in the bacterial cell and an absolutely vital part of the translation machinery. tRNAs bind amino acids and transfer them to the translating ribosomes. The binding of amino acids to tRNAs (aminoacylation or charging) is facilitated by aminoacyl tRNA synthetases. The relative abundance of different charged tRNAs is important for ensuring the fidelity of protein synthesis, because underrepresentation of the cognate charged tRNA for a given messenger RNA (mRNA) codon increases the likelihood that a near-cognate tRNA will erroneously deliver its amino acid to the growing polypeptide chain on the ribosome6. The importance of charged tRNA is reflected in the extensive response of the E. coli cell to a severe drop in the charging levels of a tRNA; the stringent response. During the stringent response the synthesis of tRNAs, ribosomal RNAs and most mRNAs is lowered in favor of transcription of specific mRNAs associated with amino acid biosynthesis and stress survival, and the growth rate of the cells is lowered dramatically7. Furthermore, recent work by us and others has shown that E. coli actively degrades the majority of its tRNA in response to stresses that limit translation4,8, suggesting that adjustment of the tRNA levels may be important for coping with such stresses. Thus, reliable measurements of tRNA abundances and charging levels will be an important tool for fully understanding bacterial stress responses.
E.coli is commonly used to express recombinant protein and due to the differences in codon usage between species, suboptimal expression is a problem often faced9. This can be circumvented by expression of additional tRNAs needed to translate the recombinant mRNA10. Measurements of tRNA charging levels in such strains could guide troubleshooting efforts and help optimize protein expression.
This method also enables the detection of &#34;mischarging&#34;; a tRNA molecule aminoacylated with a non-cognate amino acid. Aminoacylation by different amino acids may cause a tRNA to migrate with slightly different velocities through polyacrylamide gels1,11. In some cases, the method can also be used to distinguish different modification patterns on otherwise identical tRNAs3.
Another established biochemical procedure for the investigation of tRNA charging levels is periodate oxidation. The method relies on the observation that aminoacylated tRNA is protected from periodate oxidation and uncharged tRNA is not. After periodate oxidation treatment the recharging of the tRNA is used to estimate the charging levels of the harvested RNA. However, the recharging of several tRNAs has been shown to be affected by the treatment thus providing some inaccuracy12. The method presented here measures charging directly from purified RNA, thus excluding any biases from chemical or enzymatic reactions. One limitation of this method is that only one tRNA species is detected at a time, so although the same Northern blot can be stripped and reprobed for multiple tRNAs, it is time-consuming and somewhat laborious to collect data on many tRNAs.
A reliable way of normalizing samples to each other is vital in studies where the goal is to compare the relative levels of a molecule across different samples. Here we introduce a normalization procedure for RNA where a small aliquot of E. coli cells overexpressing the rare tRNAselC is added as a spike-in to all the experimental samples prior to RNA purification. This method is useful not only when examining tRNAs but for relative quantification of any species of RNA when the experimental setup is such that no endogenous RNA can be trusted to be present at the same cellular concentration in all the samples. For example, the level of a &#34;housekeeping&#34; RNA-like ribosomal RNA is often used as an endogenous reference to compare the relative quantities of another RNA between different samples13. But this is of little use if the cellular concentration of the reference RNA varies between samples, as can be the case for ribosomal RNA if sampling occurs during a stress response15,16,17 or during entry into stationary phase17. The addition of spike-in cells to the experimental samples prior to RNA purification provides a solid and accurate way of normalization independent of the sampling setup. Another way of standardization is the addition of one or more spike-in RNAs to the experimental samples after RNA purification. However, this method does not account for any differences in RNA recovery between samples.
Using E. coli cells that overexpress the reference RNA as spike-in cells (see Figure 1) in an experiment on E. coli has the drawback that it results in addition of a small amount of exogenous E. coli total RNA to the samples. We correct for this addition by analyzing a sample containing only spike-in cells in parallel with the experimental samples (see the Northern blot in Figure 2, lane labeled &#34;selC&#34;). The protocol presented is developed for E. coli K-12 but is likely to be applicable for most bacterial species.

<table>
	<tbody>
		<tr>
			<td>Urea</td>
			<td>Merck</td>
			<td>57-13-6</td>
			<td>Purity &#62;99%</td>
		</tr>
		<tr>
			<td>Polyacrylamide</td>
			<td>Serva</td>
			<td>79-06-7</td>
			<td></td>
		</tr>
		<tr>
			<td>Bis (N,N&#39;-Methylene-bis-acrylamide)</td>
			<td>BIO-RAD</td>
			<td>161-0201</td>
			<td></td>
		</tr>
		<tr>
			<td>Trichloroacetic acid (TCA)</td>
			<td>Sigma</td>
			<td>76-03-9</td>
			<td></td>
		</tr>
		<tr>
			<td>Phenol</td>
			<td>Merck</td>
			<td>108-95-2</td>
			<td></td>
		</tr>
		<tr>
			<td>IPTG</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Acetate</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tris</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrochloric acid</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NaH2PO4</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Citrate</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>SDS</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Herring Sperm DNA</td>
			<td>Sigma</td>
			<td>100403-24-5</td>
			<td></td>
		</tr>
		<tr>
			<td>BSA</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Polivinylpyrrolidone</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ficoll</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>P32 &#947;ATP</td>
			<td>Perkin Elmer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DNA oligos (probes)</td>
			<td>TAG Copenhagen</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Hybond N+ membrane</td>
			<td>GE Healthcare</td>
			<td>RPN203B</td>
			<td></td>
		</tr>
		<tr>
			<td>Crosslinker</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Electroblotter</td>
			<td>BIO-RAD</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Typhoon FLA 7000 Scanner</td>
			<td>GE Healthcare</td>
			<td>28955809</td>
			<td></td>
		</tr>
		<tr>
			<td>Spectrophotometer</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Hydridization oven</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Geiger-M&#252;ller tube</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphor imager screen</td>
			<td>GE Healthcare</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Hybridization tube</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Culture Flasks</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1.5 ml microcentrifuge tubes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>20 ml centrifuge tubes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Software</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ImageQuant</td>
			<td>GE Healthcare</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Excel</td>
			<td>Microsoft</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

quantification of the abundance and charging levels of transfer rnas in escherichia coli

Transfer RNA (tRNA) is an essential part of the translational machinery in any organism. tRNAs bind and transfer amino acids to the translating ribosome. The relative levels of different tRNAs, and the ratio of aminoacylated tRNA to total tRNA, known as the charging level, are important factors in determining the accuracy and speed of translation. Therefore, the abundance and charging levels of tRNAs are important variables to measure when studying protein synthesis, for example under various stress conditions. Here, we describe a method for harvesting tRNA and directly measuring both the relative abundance and the absolute charging level of specific tRNA species in Escherichia coli. The tRNA is harvested in such a way that the labile bond between the tRNA and its amino acid is preserved. The RNA is then subjected to gel electrophoresis and Northern blotting, which results in separation of the charged and uncharged tRNAs. The levels of specific tRNAs in different samples can be compared due to the addition of spike-in cells for normalization. Prior to RNA purification, we add 5% of E. coli cells that overproduce the rare tRNAselC to each sample. The amount of the tRNA species of interest in a sample is then normalized to the amount of tRNAselC in the same sample. Addition of spike-in cells prior to RNA purification has the advantage over addition of purified spike-in RNAs that it also accounts for any differences in cell lysis efficiency between samples.

Using the procedure described here, the abundance and charging levels of three tRNAs were measured in E. coli K-12 before and during amino acid starvation.
The arginine auxotroph strain NF9154 (thr leu his argH thi mtl supE44) was grown for at least ten generations in MOPS minimal medium supplemented with 0.4% glycerol, 50 &#181;g/mL threonine, leucine, arginine, and 5 &#181;g/mL histidi...

Watch this Scientific Journal Video about Quantification of the Abundance and Charging Levels of Transfer RNAs in Escherichia coli at JoVE.com

Quantification of the Abundance and Charging Levels of Transfer RNAs in Escherichia coli

Here we present a method for directly measuring transfer RNA charging levels from purified Escherichia coli RNA as well as a way to compare relative levels of transfer RNA, or any other short RNA, across different samples based on the addition of spike-in cells expressing a reference gene.

Quantification of the Abundance and Charging Levels of Transfer RNAs in Escherichia coli

Transfer RNA (tRNA) is an essential part of the translational machinery in any organism. tRNAs bind and transfer amino acids to the translating ribosome. ...

The overall goal of this experiment is to quantify the abundance and charging levels of transfer RNAs in Escherichia coli. This method can help answer key questions in cell biology such as, how tRNA charging levels changes at different growth states. The main advantage of this method is that, RNA levels can be quantitatively compared even between growth states that drastically alter the composition of the RNA in the cells.Start this experiment by growing experimental and spike-in E.coli cultures according to the text protocol. Grow the spike-in culture at 37 degree celsius, while shaking at 160 RPM. When the spike-in culture has reached an OD436 of about 0.1, induce the expression of tRNA cell C by adding IPTG.Grow the culture until it reaches an OD436 of about 0.5. Then, move the culture to ice until all samples have been harvested. After that, prewarm one 100 milliliter capped culture flask containing four milliliters of 10%TCA for each sample in a 37 degree celsius water bath.Measure and record the OD436 of the experimental cultures directly before cell harvest. Then, transfer four milliliters of culture to a prewarmed TCA containing flask. Mix the sample by hand swirling the flask for five seconds, which will immediately disable all enzymatic activities preserving the charging levels of the tRNAs.When all samples have been collected, add 5%spike-in cells to each sample. Also prepare a control sample consisting only of spike-in cells as described in the text protocol. To start RNA extraction, pour eight milliliters of each sample, including controls into an ice chilled centrifuge tube.Centrifuge the samples at 9, 500 x G at four degree celsius for 10 minutes. After removing the supernatant completely, re-suspend the pellet in 0.3 milliliters of cold sodium acetate, containing 10 millilimolar EDTA. Transfer each samples into a cold 1.5 milliliter microcentrifuge tube and add 0.3 milliliters of phenol equilibrated with the buffer, used to re-suspend the pellet.Then, vortex each sample 10 times for 15 seconds each time. With at least one minute at zero degree celsius between each vortex, to keep the samples cold. Next, centrifuge the samples at 20, 000 x G at four degree celsius for 15 minutes.Transfer the upper or water face to a new 1.5 milliliter microcentrifuge tube. Add 0.3 milliliters of cold phenol to the water face and vortex the samples four times 15 seconds each as previously described. Then, centrifuge the samples at 20, 000 x G at four degrees celsius for 10 minutes.Transfer the water face to a new cold 1.5 milliliter microcentrifuge tube and add 2.5 volumes of cold 96%ethanol. Then, incubate the tubes at 20 degree celsius for one hour to precipitate the RNA. Centrifuge the samples at 20, 000 x G at four degree celsius for 30 minutes.After removing the supernatant, carefully add one milliliter of cold 70%ethanol to the RNA pellet, making sure not to disturb it. Invert the tube gently once, to wash it with ethanol. Finally, centrifuge at 20, 000 x G at four degree celsius for 10 minutes.Remove the supernatant completely, and air dry the pellet until the ethanol is completely removed. At 20 microliters of cold sodium acetate containing 1 millimolar EDTA, vortex vigorously to re-suspend the pellet. To start electrophoresis, mix four microliters of each sample with six microliters of loading buffer.Load the samples including controls onto a 0.4 millimeter thick 6.5 polyacrylamide gel containing eight molar ureal and 0.1 molar sodium acetate buffer. Then, separate the RNA by running the electrophoresis at 10 volts per centimeter of gel at four degree celsius for approximately 20 hours until the bromophenol blue dye reaches the bottom of the gel. Carefully separate the two glass plates so that the gel remains on one of them.Use the gel area from the xylene cyanol dye and 20 centimeters down towards the bromophenol dye for blotting. Cut a thin piece of filter paper to the size of the desired blotting area. Place the filter paper on top of the part of the gel that will be used for blotting.Cut off and discard the parts of the gel not covered with filter paper. Then use the filter paper to carefully lift the gel away from the glass plate. Place a positively charged nylon membrane on top of the gel, and electroblot it in transfer buffer at 20 volts for 90 minutes.Finish by crosslinking the RNA to the membrane using UV light. Next, place the crosslinked membrane in a hybridization tube and add six milliliters of hybridization solution. Rotate the tube at 42 degree celsius for one hour to pre-hybridize the membrane.Then, add 30 peak molar radioactive oligo DNA probe, five prime and labeled with P32. Rotate to incubate the membrane with the probe at 42 degree celsius overnight. After incubation, use a disposable 10 milliliter pipette to remove the probe.Next, quickly wash the membrane twice in the hybridization tube, in 15 milliliters of washing solution at room temperature. Move the membrane to a flat plastic container, cover it with the washing solution and close the lid. Incubate the membrane on a shaker at room temperature for 30 minutes.Change the solution and continue washing until achieving a satisfying signal to noise ratio. Use a geiger muller tube to obtain the signal to noise ratio, by comparing the radiation from the area where the probe has hybridized to tRNA, to the radiation from an empty area. After that, wrap the membrane tightly in plastic wrap and seal it airtight by welding.Place this membrane on a phosphorimaging screen. After adequate exposure time, scan the screen using a laser scanner and save the file in gel format. Next, load the gel file into the imaging software.Draw a vertical line along each of the sample lanes so that it spans most of the width of the lane while excluding the edges of the bands where the signal can be uneven. To visualize counts from each lane, click analysis and then, create graph. Manually define the two peaks that represent the charged and the uncharged tRNA from each lane.After that, click on analysis and then, area report to obtain counts from each peak. Finally, record the area under each of the two peaks. Calculate the tRNA levels as described in the text protocol.This method was used to measure the abundance of various tRNAs and E.Coli nf915 before and during our arginine starvation. On the northern plot hybridized with different tRNA probes, there is a clear separation between the bands that represent the charge tRNA from the bands that represent the uncharged tRNA. The radiation profile along each lane, was obtained from the northern blots using imaging software.The radiation signal from each lane was quantified by isolating each from the blot. A graph that represents the quantification of the signal from a single lane, shows two peaks. The left peak comes from the aminoacylated tRNA and the right from the deacylated tRNA.The area under each peak is exported for further analysis. Quantification of the bands from the northern blot, shows that the relative abundance of all tested tRNA species rapidly and significantly decreased during amino acid starvation. On the other hand, tRNA charging levels of the arginine accepting tRNA dropped rapidly upon arginine removal and then slightly increased during the starvation period.However, the charging levels of the other tRNAs increased slightly upon starvation and then decreased to almost pre-starvation levels. After watching this video, you should have a good understanding of how to purify RNA in a way that tRNA charging and abundance can be quantified and how to use spike-in cells for normalization. Throughout this procedure, it's important to remember to keep the RNA cold and acidic to prevent the hydrolysis of the RNA.

quantification-abundance-charging-levels-transfer-rnas-escherichia

Research

JoVE Journal

Biochemistry

9.2K ビュー.  University of Copenhagen. The overall goal of this experiment is to quantify the abundance and charging levels of transfer RNAs in Escherichia coli. This method can help answer key questions in cell biology such as, how tRNA charging levels changes at different growth states. The main advantage of this method is that, RNA levels can be quantitatively compared even between growth states that drastically alter the composition of the RNA in the cells.Start this experiment by growing experimental and spike-in E.col...

ビデオ: Quantification of the Abundance and Charging Levels of Transfer RNAs in Escherichia coli

Directed Protein Packaging within Outer Membrane Vesicles from Escherichia coli: Design, Production and Purification

An increasing interest in applying synthetic biology techniques to program outer membrane vesicles (OMV) are leading to some very interesting and unique applications for OMV where traditional nanoparticles are proving too difficult to synthesize. To date, all Gram-negative bacteria have been shown to produce OMV demonstrating packaging of a variety of cargo that includes small molecules, peptides, proteins and genetic material. Based on their diverse cargo, OMV are implicated in many biological processes ranging from cell-cell communication to gene transfer and delivery of virulence factors depending upon which bacteria are producing the OMV. Only recently have bacterial OMV become accessible for use across a wide range of applications through the development of techniques to control and direct packaging of recombinant proteins into OMV. This protocol describes a method for the production, purification, and use of enzyme packaged OMV providing for improved overall production of recombinant enzyme, increased vesiculation, and enhanced enzyme stability. Successful utilization of this protocol will result in the creation of a bacterial strain that simultaneously produces a recombinant protein and directs it for OMV encapsulation through creating a synthetic linkage between the recombinant protein and an outer membrane anchor protein. This protocol also details methods for isolating OMV from bacterial cultures as well as proper handling techniques and things to consider when adapting this protocol for use for other unique applications such as: pharmaceutical drug delivery, medical diagnostics, and environmental remediation.

Directed Protein Packaging within Outer Membrane Vesicles from Escherichia coli: Design, Production and Purification

A protocol for the production, purification, and use of enzyme packaged outer membrane vesicles (OMV) providing for enhanced enzyme stability for implementation across diverse applications is presented.

An increasing interest in applying synthetic biology techniques to program outer membrane vesicles (OMV) are leading to some very interesting and unique ...

Detection of the pH-dependent Activity of Escherichia coli Chaperone HdeB In Vitro and In Vivo

Bacteria are frequently exposed to environmental changes, such as alterations in pH, temperature, redox status, light exposure or mechanical force. Many of these conditions cause protein unfolding in the cell and have detrimental impact on the survival of the organism. A group of unrelated, stress-specific molecular chaperones have been shown to play essential roles in the survival of these stress conditions. While fully folded and chaperone-inactive before stress, these proteins rapidly unfold and become chaperone-active under specific stress conditions. Once activated, these conditionally disordered chaperones bind to a large number of different aggregation-prone proteins, prevent their aggregation and either directly or indirectly facilitate protein refolding upon return to non-stress conditions. The primary approach for gaining a more detailed understanding about the mechanism of their activation and client recognition involves the purification and subsequent characterization of these proteins using in vitro chaperone assays. Follow-up in vivo stress assays are absolutely essential to independently confirm the obtained in vitro results.
This protocol describes in vitro and in vivo methods to characterize the chaperone activity of E. coli HdeB, an acid-activated chaperone. Light scattering measurements were used as a convenient read-out for HdeB&#39;s capacity to prevent acid-induced aggregation of an established model client protein, MDH, in vitro. Analytical ultracentrifugation experiments were applied to reveal complex formation between HdeB and its client protein LDH, to shed light into the fate of client proteins upon their return to non-stress conditions. Enzymatic activity assays of the client proteins were conducted to monitor the effects of HdeB on pH-induced client inactivation and reactivation. Finally, survival studies were used to monitor the influence of HdeB&#39;s chaperone function in vivo.

Detection of the pH-dependent Activity of Escherichia coli Chaperone HdeB In Vitro and In Vivo

This study describes biophysical, biochemical and molecular techniques to characterize the chaperone activity of Escherichia coli HdeB under acidic pH conditions. These methods have been successfully applied for other acid-protective chaperones such as HdeA and can be modified to work for other chaperones and stress conditions.

Bacteria are frequently exposed to environmental changes, such as alterations in pH, temperature, redox status, light exposure or mechanical force. Many ...

Quantification of Hypopigmentation Activity In Vitro

This study presents laboratory methods for the quantification of hypopigmentation activity in vitro. Melanin, the major pigment in melanocytes, is synthesized in response to multiple cellular and environmental factors. Melanin protects skin cells from ultraviolet damage, but also has biophysical and biochemical functions. Excessive production or accumulation of melanin in melanocytes can cause dermatological problems, such as freckles, dark spots, melasma, and moles. Therefore, the control of melanogenesis with hypopigmentation agents is important in individuals with clinical or cosmetic needs. Melanin is primarily synthesized in the melanosomes of melanocytes in a complex biochemical process called melanogenesis, which is influenced by extrinsic and intrinsic factors, such as hormones, inflammation, age, and ultraviolet light exposure. We describe three methods to determine the hypopigmentation activity of chemicals or natural substances in melanocytes: measurement of the 1) cellular tyrosinase activity and 2) melanin content, and 3) staining and quantifying cellular melanin with image analysis.
In melanogenesis, tyrosinase catalyzes the rate-limiting step that converts L-tyrosine into 3,4-dihydroxyphenylalanine (L-DOPA) and then into dopaquinone. Therefore, the inhibition of tyrosinase is a primary hypopigmentation mechanism. In cultured melanocytes, tyrosinase activity can be quantified by adding L-DOPA as a substrate and measuring dopaquinone production by spectrophotometry. Melanogenesis can also be measured by quantifying the melanin content. The melanin-containing cellular fraction is extracted with NaOH and melanin is quantified spectrophotometrically. Finally, the melanin content can be quantified by image analysis following Fontana-Masson staining of melanin. Although the results of these in vitro assays may not always be reproduced in human skin, these methods are widely used in melanogenesis research, especially as the initial step to identify potential hypopigmentation activity. These methods can also be used to assess melanocyte activity, growth, and differentiation. Consistent results with the three different methods ensure the validity of the effects.

We describe three experimental methods for evaluating the hypopigmentation activity of chemicals in vitro: quantification of 1) cellular tyrosinase activity and 2) melanin content, and 3) measurement of melanin by cellular melanin staining and image analysis.

This study presents laboratory methods for the quantification of hypopigmentation activity in vitro. Melanin, the major pigment in melanocytes, is ...

Large-scale Production of Recombinant RNAs on a Circular Scaffold Using a Viroid-derived System in Escherichia coli

With increasing interest in RNA biology and the use of RNA molecules in sophisticated biotechnological applications, the methods to produce large amounts of recombinant RNAs are limited. Here, we describe a protocol to produce large amounts of recombinant RNA in Escherichia coli based on co-expression of a chimeric molecule that contains the RNA of interest in a viroid scaffold and a plant tRNA ligase. Viroids are relatively small, non-coding, highly base-paired circular RNAs that are infectious to higher plants. The host plant tRNA ligase is an enzyme recruited by viroids that belong to the family Avsunviroidae, such as Eggplant latent viroid (ELVd), to mediate RNA circularization during viroid replication. Although ELVd does not replicate in E. coli, an ELVd precursor is efficiently transcribed by the E. coli RNA polymerase and processed by the embedded hammerhead ribozymes in bacterial cells, and the resulting monomers are circularized by the co-expressed tRNA ligase reaching a remarkable concentration. The insertion of an RNA of interest into the ELVd scaffold enables the production of tens of milligrams of the recombinant RNA per liter of bacterial culture in regular laboratory conditions. A main fraction of the RNA product is circular, a feature that facilitates the purification of the recombinant RNA to virtual homogeneity. In this protocol, a complementary DNA (cDNA) corresponding to the RNA of interest is inserted in a particular position of the ELVd cDNA in an expression plasmid that is used, along the plasmid to co-express eggplant tRNA ligase, to transform E. coli. Co-expression of both molecules under the control of strong constitutive promoters leads to production of large amounts of the recombinant RNA. The recombinant RNA can be extracted from the bacterial cells and separated from the bulk of bacterial RNAs taking advantage of its circularity.

Large-scale Production of Recombinant RNAs on a Circular Scaffold Using a Viroid-derived System in Escherichia coli

Here, we present a protocol to produce large amounts of recombinant RNA in Escherichia coli by co-expressing a chimeric RNA that contains the RNA of interest in a viroid scaffold and a plant tRNA ligase. The main product is a circular molecule that facilitates purification to homogeneity.

With increasing interest in RNA biology and the use of RNA molecules in sophisticated biotechnological applications, the methods to produce large amounts ...

Site-Directed Mutagenesis for In Vitro and In Vivo Experiments Exemplified with RNA Interactions in Escherichia Coli

Site-directed mutagenesis is a technique used to introduce specific mutations in DNA to investigate the interaction between small non-coding ribonucleic acid (sRNA) molecules and target messenger RNAs (mRNAs). In addition, site-directed mutagenesis is used to map specific protein binding sites to RNA. A 2-step and 3-step PCR based introduction of mutations is described. The approach is relevant to all protein-RNA and RNA-RNA interaction studies. In short, the technique relies on designing primers with the desired mutation(s), and through 2 or 3 steps of PCR synthesizing a PCR product with the mutation. The PCR product is then used for cloning. Here, we describe how to perform site-directed mutagenesis with both the 2- and 3-step approach to introduce mutations to the sRNA, McaS, and the mRNA, csgD, to investigate RNA-RNA and RNA-protein interactions. We apply this technique to investigate RNA interactions; however, the technique is applicable to all mutagenesis studies (e.g., DNA-protein interactions, amino-acid substitution/deletion/addition). It is possible to introduce any kind of mutation except for non-natural bases but the technique is only applicable if a PCR product can be used for downstream application (e.g., cloning and template for further PCR).

Site-Directed Mutagenesis for In Vitro and In Vivo Experiments Exemplified with RNA Interactions in Escherichia Coli

Site-directed mutagenesis is a technique used to introduce specific mutations in deoxyribonucleic acid (DNA). This protocol describes how to do site-directed mutagenesis with a 2-step and 3-step polymerase chain reaction (PCR) based approach, which is applicable to any DNA fragment of interest.

Site-directed mutagenesis is a technique used to introduce specific mutations in DNA to investigate the interaction between small non-coding ribonucleic ...

Use of Alu Element Containing Minigenes to Analyze Circular RNAs

In addition to linear mRNAs, many eukaryotic genes generate circular RNAs. Most circular RNAs are generated by joining a 5&#39; splice site with an upstream 3&#39; splice site within a pre-mRNA, a process called back-splicing. This circularization is likely aided by secondary structures in the pre-mRNA that bring the splice sites into close proximity. In human genes, Alu elements are thought to promote these secondary RNA structures, as Alu elements are abundant and exhibit base complementarities with each other when present in opposite directions in the pre-mRNA. Here, we describe the generation and analysis of large, Alu element containing reporter genes that form circular RNAs. Through optimization of cloning protocols, reporter genes with up to 20 kb insert length can be generated. Their analysis in co-transfection experiments allows the identification of regulatory factors. Thus, this method can identify RNA sequences and cellular components involved in circular RNA formation.

Use of Alu Element Containing Minigenes to Analyze Circular RNAs

We clone and analyze reporter genes generating circular RNAs. These reporter genes are larger than constructs to analyze linear splicing and contain Alu elements. To investigate the circular RNAs, the constructs are transfected into cells and resulting RNA is analyzed using RT-PCR after removal of linear RNA.

In addition to linear mRNAs, many eukaryotic genes generate circular RNAs. Most circular RNAs are generated by joining a 5&#39; splice site with an ...

Characterization of Membrane Transporters by Heterologous Expression in E. coli and Production of Membrane Vesicles

Several methods have been developed to functionally characterize novel membrane transporters. Polyamines are ubiquitous in all organisms, but polyamine exchangers in plants have not been identified. Here, we outline a method to characterize polyamine antiporters using membrane vesicles generated from the lysis of Escherichia coli cells heterologously expressing a plant antiporter. First, we heterologously expressed AtBAT1 in an E. coli strain deficient in polyamine and arginine exchange transporters. Vesicles were produced using a French press, purified by ultracentrifugation and utilized in a membrane filtration assay of labeled substrates to demonstrate the substrate specificity of the transporter. These assays demonstrated that AtBAT1 is a proton-mediated transporter of arginine, &#947;-aminobutyric acid (GABA), putrescine and spermidine. The mutant strain that was developed for the assay of AtBAT1 may be useful for the functional analysis of other families of plant and animal polyamine exchangers. We also hypothesize that this approach can be used to characterize many other types of antiporters, as long as these proteins can be expressed in the bacterial cell membrane. E. coli is a good system for the characterization of novel transporters, since there are multiple methods that can be employed to mutagenize native transporters.

Characterization of Membrane Transporters by Heterologous Expression in E. coli and Production of Membrane Vesicles

We describe a method for the characterization of proton-driven membrane transporters in membrane vesicle preparations produced by heterologous expression in E. coli and lysis of cells using a French press.

Several methods have been developed to functionally characterize novel membrane transporters. Polyamines are ubiquitous in all organisms, but polyamine ...

Quantification of Coenzyme A in Cells and Tissues

Emerging research has revealed that the cellular coenzyme A (CoA) supply can become limiting with a detrimental impact on growth, metabolism and survival. Measurement of cellular CoA is a challenge due to its relatively low abundance and the dynamic conversion of free CoA to CoA thioesters that, in turn, participate in numerous metabolic reactions. A method is described that navigates through potential pitfalls during sample preparation to yield an assay with a broad linear range of detection that is suitable for use in many biomedical laboratories.

This method describes sample preparation from cultured cells and animal tissues, extraction and derivatization of coenzyme A in the samples, followed by high pressure liquid chromatography for purification and quantification of the derivatized coenzyme A by absorbance or fluorescence detection.

Emerging research has revealed that the cellular coenzyme A (CoA) supply can become limiting with a detrimental impact on growth, metabolism and survival. ...

Site Specific Lysine Acetylation of Histones for Nucleosome Reconstitution using Genetic Code Expansion in Escherichia coli

Acetylated histone proteins can be easily expressed in Escherichia coli encoding a mutant, N&#949;-acetyl-lysine (AcK)-specific Methanosarcina mazi pyrrolysine tRNA-synthetase (MmAcKRS1) and its cognate tRNA (tRNAPyl) to assemble reconstituted mononucleosomes with site specific acetylated histones. MmAcKRS1 and tRNAPyl deliver AcK at an amber mutation site in the mRNA of choice during translation in Escherichia coli. This technique has been used extensively to incorporate AcK at H3 lysine sites. Pyrrolysyl-tRNA synthetase (PylRS) can also be easily evolved to incorporate other noncanonical amino acids (ncAAs) for site specific protein modification or functionalization. Here we detail a method to incorporate AcK using the MmAcKRS1 system into histone H3 and integrate acetylated H3 proteins into reconstituted mononucleosomes. Acetylated reconstituted mononucleosomes can be used in biochemical and binding assays, structure determination, and more. Obtaining modified mononucleosomes is crucial for designing experiments related to discovering new interactions and understanding epigenetics.

Site Specific Lysine Acetylation of Histones for Nucleosome Reconstitution using Genetic Code Expansion in Escherichia coli

Here we present a method to express acetylated histone proteins using genetic code expansion and assemble reconstituted nucleosomes in vitro.

Acetylated histone proteins can be easily expressed in Escherichia coli encoding a mutant, N&#949;-acetyl-lysine (AcK)-specific Methanosarcina mazi ...

Extraction and Visualization of Protein Aggregates after Treatment of Escherichia coli with a Proteotoxic Stressor

The exposure of living organisms to environmental and cellular stresses often causes disruptions in protein homeostasis and can result in protein aggregation. The accumulation of protein aggregates in bacterial cells can lead to significant alterations in the cellular phenotypic behavior, including a reduction in growth rates, stress resistance, and virulence. Several experimental procedures exist for the examination of these stressor-mediated phenotypes. This paper describes an optimized assay for the extraction and visualization of aggregated and soluble proteins from different Escherichia coli strains after treatment with a silver-ruthenium-containing antimicrobial. This compound is known to generate reactive oxygen species and causes widespread protein aggregation. 
The method combines a centrifugation-based separation of protein aggregates and soluble proteins from treated and untreated cells with subsequent separation and visualization by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Coomassie staining. This approach is simple, fast, and allows a qualitative comparison of protein aggregate formation in different E. coli strains. The methodology has a wide range of applications, including the possibility to investigate the impact of other proteotoxic antimicrobials on in vivo protein aggregation in a wide range of bacteria. Moreover, the protocol can be used to identify genes that contribute to increased resistance to proteotoxic substances. Gel bands can be used for the subsequent identification of proteins that are particularly prone to aggregation.

Extraction and Visualization of Protein Aggregates after Treatment of Escherichia coli with a Proteotoxic Stressor

This protocol describes the extraction and visualization of aggregated and soluble proteins from Escherichia coli after treatment with a proteotoxic antimicrobial. Following this procedure allows a qualitative comparison of protein aggregate formation in vivo in different bacterial strains and/or between treatments.