Gene Symbol: ssrA
Description: miscRNA
Alias: ECK2617, JWR0055, sipB
Species: Escherichia coli str. K-12 substr. MG1655

Top Publications

  1. Roche E, Sauer R. SsrA-mediated peptide tagging caused by rare codons and tRNA scarcity. EMBO J. 1999;18:4579-89 pubmed
    b>SsrA RNA mediates the addition of a C-terminal peptide tag (AANDENYALAA) to bacterial proteins translated from mRNAs without in-frame stop codons...
  2. Keiler K, Waller P, Sauer R. Role of a peptide tagging system in degradation of proteins synthesized from damaged messenger RNA. Science. 1996;271:990-3 pubmed
    ..b562 translated from messenger RNAs without stop codons were modified by carboxyl terminal addition of an ssrA-encoded peptide tag and subsequently degraded by carboxyl terminal-specific proteases present in both the cytoplasm ..
  3. Ivanova N, Lindell M, Pavlov M, Holmberg Schiavone L, Wagner E, Ehrenberg M. Structure probing of tmRNA in distinct stages of trans-translation. RNA. 2007;13:713-22 pubmed
    ..Our findings suggest that, in vivo, a dominant fraction of tmRNA is in complex with SmpB and that, in vitro, SmpB remains tmRNA bound at the initial steps of trans-translation. ..
  4. Roche E, Sauer R. Identification of endogenous SsrA-tagged proteins reveals tagging at positions corresponding to stop codons. J Biol Chem. 2001;276:28509-15 pubmed
    The SsrA.SmpB quality control system adds a C-terminal degradation peptide (AANDENYALAA) to nascent chains on stalled ribosomes, thereby freeing the ribosome and ensuring proteolysis of the tagged protein...
  5. Burks J, Zwieb C, Muller F, Wower I, Wower J. Comparative 3-D modeling of tmRNA. BMC Mol Biol. 2005;6:14 pubmed
    ..These models will guide in the design of experiments and provide a better understanding of trans-translation. The comparative procedure described here for tmRNA is easily adopted for the modeling the members of other RNA families. ..
  6. Withey J, Friedman D. A salvage pathway for protein structures: tmRNA and trans-translation. Annu Rev Microbiol. 2003;57:101-23 pubmed
    Transfer-messenger RNA (tmRNA, or SsrA), found in all eubacteria, has both transfer and messenger RNA activity...
  7. Yamamoto Y, Sunohara T, Jojima K, Inada T, Aiba H. SsrA-mediated trans-translation plays a role in mRNA quality control by facilitating degradation of truncated mRNAs. RNA. 2003;9:408-18 pubmed
    An important unsolved question regarding the bacterial SsrA system is the fate of target mRNAs replaced by SsrA RNA during trans-translation...
  8. Williams K, Bartel D. Phylogenetic analysis of tmRNA secondary structure. RNA. 1996;2:1306-10 pubmed
  9. Ivanova N, Pavlov M, Felden B, Ehrenberg M. Ribosome rescue by tmRNA requires truncated mRNAs. J Mol Biol. 2004;338:33-41 pubmed
    ..We conclude that tmRNA action in vivo must always be preceded by mRNA truncation, and suggest that cleavage of ribosome bound mRNAs is a common element in different bacterial stress responses. ..

More Information


  1. Zwieb C, Wower I, Wower J. Comparative sequence analysis of tmRNA. Nucleic Acids Res. 1999;27:2063-71 pubmed
    ..Described are the conserved and variable features of the tmRNAs from a wide phylogenetic spectrum, the structural properties specific to the bacterial subgroups and preliminary 3-dimensional models from the pseudoknotted regions. ..
  2. Flynn J, Levchenko I, Seidel M, Wickner S, Sauer R, Baker T. Overlapping recognition determinants within the ssrA degradation tag allow modulation of proteolysis. Proc Natl Acad Sci U S A. 2001;98:10584-9 pubmed
    The ssrA tag, an 11-aa peptide added to the C terminus of proteins stalled during translation, targets proteins for degradation by ClpXP and ClpAP...
  3. Muto A, Ushida C, Himeno H. A bacterial RNA that functions as both a tRNA and an mRNA. Trends Biochem Sci. 1998;23:25-9 pubmed
    ..The result is a chimeric protein with the tag peptide attached to the C-terminus of the truncated peptide. ..
  4. Farrell C, Grossman A, Sauer R. Cytoplasmic degradation of ssrA-tagged proteins. Mol Microbiol. 2005;57:1750-61 pubmed
    Degradation of ssrA-tagged proteins is a central feature of protein-quality control in all bacteria...
  5. Karzai A, Roche E, Sauer R. The SsrA-SmpB system for protein tagging, directed degradation and ribosome rescue. Nat Struct Biol. 2000;7:449-55 pubmed
    Bacteria contain a remarkable RNA molecule - known alternatively as SsrA RNA, tmRNA, or 10Sa RNA - that acts both as a tRNA and as an mRNA to direct the modification of proteins whose biosynthesis has stalled or has been interrupted...
  6. Keiler K, Shapiro L, Williams K. tmRNAs that encode proteolysis-inducing tags are found in all known bacterial genomes: A two-piece tmRNA functions in Caulobacter. Proc Natl Acad Sci U S A. 2000;97:7778-83 pubmed rescue stalled ribosomes and to clear the cell of incomplete polypeptides involves an RNA species, tmRNA (SsrA), which functions as both a tRNA and an mRNA...
  7. McGinness K, Baker T, Sauer R. Engineering controllable protein degradation. Mol Cell. 2006;22:701-7 pubmed
    ..In E. coli, the adaptor SspB tethers ssrA-tagged substrates to the ClpXP protease, causing a modest increase in their rate of degradation...
  8. Valle M, Gillet R, Kaur S, Henne A, Ramakrishnan V, Frank J. Visualizing tmRNA entry into a stalled ribosome. Science. 2003;300:127-30 pubmed publisher
    ..The structure reveals how tmRNA could move through the ribosome despite its complicated topology and also suggests roles for proteins S1 and SmpB in the function of tmRNA...
  9. Barends S, Karzai A, Sauer R, Wower J, Kraal B. Simultaneous and functional binding of SmpB and EF-Tu-TP to the alanyl acceptor arm of tmRNA. J Mol Biol. 2001;314:9-21 pubmed
    ..Therefore, SmpB may function as an essential modulator of the tRNA-like acceptor arm of tmRNA during its successive steps in trans-translation. ..
  10. Gottesman S, Roche E, Zhou Y, Sauer R. The ClpXP and ClpAP proteases degrade proteins with carboxy-terminal peptide tails added by the SsrA-tagging system. Genes Dev. 1998;12:1338-47 pubmed
    ..This modification is mediated by SsrA RNA (also called 10Sa RNA and tmRNA) and marks the tagged polypeptide for proteolysis...
  11. Karzai A, Sauer R. Protein factors associated with the SsrA.SmpB tagging and ribosome rescue complex. Proc Natl Acad Sci U S A. 2001;98:3040-4 pubmed
    b>SsrA RNA acts as a tRNA and mRNA to modify proteins whose synthesis on ribosomes has stalled...
  12. Withey J, Friedman D. Analysis of the role of trans-translation in the requirement of tmRNA for lambdaimmP22 growth in Escherichia coli. J Bacteriol. 1999;181:2148-57 pubmed
    The small, stable RNA molecule encoded by ssrA, known as tmRNA or 10Sa RNA, is required for the growth of certain hybrid lambdaimmP22 phages in Escherichia coli...
  13. Zwieb C, Gorodkin J, Knudsen B, Burks J, Wower J. tmRDB (tmRNA database). Nucleic Acids Res. 2003;31:446-7 pubmed
    ..Three-dimensional models of the tmRNAs and their associated proteins in PDB format give evidence for the recent progress that has been made in the understanding of tmRNP structure and function. ..
  14. Pedersen K, Zavialov A, Pavlov M, Elf J, Gerdes K, Ehrenberg M. The bacterial toxin RelE displays codon-specific cleavage of mRNAs in the ribosomal A site. Cell. 2003;112:131-40 pubmed
    ..We suggest that inhibition of protein synthesis by RelE is reversed with the help of tmRNA, and that RelE plays a regulatory role in bacteria during adaptation to poor growth conditions. ..
  15. Collier J, Binet E, Bouloc P. Competition between SsrA tagging and translational termination at weak stop codons in Escherichia coli. Mol Microbiol. 2002;45:745-54 pubmed
    b>SsrA is a tmRNA involved in tagging polypeptides on stalled ribosomes. The resulting fusion proteins are then degraded. We purified endogenous SsrA-tagged proteins by means of a genetically engineered SsrA and identified some of them...
  16. Hanawa Suetsugu K, Bordeau V, Himeno H, Muto A, Felden B. Importance of the conserved nucleotides around the tRNA-like structure of Escherichia coli transfer-messenger RNA for protein tagging. Nucleic Acids Res. 2001;29:4663-73 pubmed
    ..Overall, the highly conserved nucleotides around the tRNA-like portion are maintained for both structural and functional requirements during evolution. ..
  17. Andersen E, Rosenblad M, Larsen N, Westergaard J, Burks J, Wower I, et al. The tmRDB and SRPDB resources. Nucleic Acids Res. 2006;34:D163-8 pubmed publisher
    ..All alignments can be easily examined using a new exploratory browser. The databases provide links to high-resolution structures and serve as depositories for structures obtained by molecular modeling...
  18. Felden B, Gesteland R, Atkins J. Eubacterial tmRNAs: everywhere except the alpha-proteobacteria?. Biochim Biophys Acta. 1999;1446:145-8 pubmed
    ..Remarkably, tmDNA sequences could be amplified from all species tested apart from those in the alpha-Proteobacteria, raising evolutionary implications. ..
  19. Lee S, Bailey S, Apirion D. Small stable RNAs from Escherichia coli: evidence for the existence of new molecules and for a new ribonucleoprotein particle containing 6S RNA. J Bacteriol. 1978;133:1015-23 pubmed
    ..5S RNA was less stable. On the other hand, purified 6S RNA was more susceptible than tRNA to cell nucleases when incubated with cell extracts, suggesting that, being in a particle, it is protected from cell nucleases. ..
  20. Williams K, Martindale K, Bartel D. Resuming translation on tmRNA: a unique mode of determining a reading frame. EMBO J. 1999;18:5423-33 pubmed
    ..switches from an mRNA lacking an in-frame stop codon and resumes translation on a specialized RNA known as tmRNA, SsrA or 10Sa RNA...
  21. Karzai A, Susskind M, Sauer R. SmpB, a unique RNA-binding protein essential for the peptide-tagging activity of SsrA (tmRNA). EMBO J. 1999;18:3793-9 pubmed
    In bacteria, SsrA RNA recognizes ribosomes stalled on defective messages and acts as a tRNA and mRNA to mediate the addition of a short peptide tag to the C-terminus of the partially synthesized nascent polypeptide chain...
  22. Singh N, Varshney U. A physiological connection between tmRNA and peptidyl-tRNA hydrolase functions in Escherichia coli. Nucleic Acids Res. 2004;32:6028-37 pubmed
    The bacterial ssrA gene codes for a dual function RNA, tmRNA, which possesses tRNA-like and mRNA-like regions...
  23. Felden B, Hanawa K, Atkins J, Himeno H, Muto A, Gesteland R, et al. Presence and location of modified nucleotides in Escherichia coli tmRNA: structural mimicry with tRNA acceptor branches. EMBO J. 1998;17:3188-96 pubmed
    ..coli tmRNA suggests that one or both of these post-transcriptional modifications may be required for optimal stability of the acceptor branch which is needed for efficient aminoacylation. ..
  24. Konno T, Kurita D, Takada K, Muto A, Himeno H. A functional interaction of SmpB with tmRNA for determination of the resuming point of trans-translation. RNA. 2007;13:1723-31 pubmed
    ..A mutant SmpB with a truncation of the unstructured C-terminal tail failed to promote peptidyl transfer, although it still protected U(85) from chemical modification. ..
  25. Hayes C, Bose B, Sauer R. Stop codons preceded by rare arginine codons are efficient determinants of SsrA tagging in Escherichia coli. Proc Natl Acad Sci U S A. 2002;99:3440-5 pubmed
    The SsrA or tmRNA quality control system intervenes when ribosomes stall on mRNAs and directs the addition of a C-terminal peptide tag that targets the modified polypeptide for degradation...
  26. Gutmann S, Haebel P, Metzinger L, Sutter M, Felden B, Ban N. Crystal structure of the transfer-RNA domain of transfer-messenger RNA in complex with SmpB. Nature. 2003;424:699-703 pubmed publisher
    ..On the basis of this structure, we propose a model for the binding of tmRNA on the ribosome...
  27. Nameki N, Tadaki T, Himeno H, Muto A. Three of four pseudoknots in tmRNA are interchangeable and are substitutable with single-stranded RNAs. FEBS Lett. 2000;470:345-9 pubmed
    ..Together with an earlier study showing the significance of PK1, it is concluded that among the four pseudoknots, PK1 is the most functional. ..
  28. Barends S, Wower J, Kraal B. Kinetic parameters for tmRNA binding to alanyl-tRNA synthetase and elongation factor Tu from Escherichia coli. Biochemistry. 2000;39:2652-8 pubmed
    ..These observations can be interpreted to suggest that additional factors facilitate tmRNA binding to ribosomes. ..
  29. Nameki N, Felden B, Atkins J, Gesteland R, Himeno H, Muto A. Functional and structural analysis of a pseudoknot upstream of the tag-encoded sequence in E. coli tmRNA. J Mol Biol. 1999;286:733-44 pubmed
    ..Nucleotide insertion or deletion between the pseudoknot and the coding sequence do not change the mRNA frame of the tag-peptide sequence, suggesting that the pseudoknot structure is not a determinant for the resumption of translation. ..
  30. Wower I, Zwieb C, Wower J. Contributions of pseudoknots and protein SmpB to the structure and function of tmRNA in trans-translation. J Biol Chem. 2004;279:54202-9 pubmed
    ..Taken together, these results provide unanticipated insights into the functions of the pseudoknots and protein SmpB during tmRNA folding, maturation, and protein synthesis. ..
  31. Himeno H, Sato M, Tadaki T, Fukushima M, Ushida C, Muto A. In vitro trans translation mediated by alanine-charged 10Sa RNA. J Mol Biol. 1997;268:803-8 pubmed
    ..The dual function of 10Sa RNA both as an mRNA and as a tRNA in vitro strongly supports the trans translation hypothesis. ..
  32. Komine Y, Kitabatake M, Yokogawa T, Nishikawa K, Inokuchi H. A tRNA-like structure is present in 10Sa RNA, a small stable RNA from Escherichia coli. Proc Natl Acad Sci U S A. 1994;91:9223-7 pubmed
    ..The purified 10Sa RNA can be charged with alanine in vitro. Disruption of the gene encoding 10Sa RNA (ssrA) caused a reduction in the rate of cell growth, which was especially apparent at 45 degrees C, and a reduction in ..
  33. Chauhan A, Apirion D. The gene for a small stable RNA (10Sa RNA) of Escherichia coli. Mol Microbiol. 1989;3:1481-5 pubmed
    ..It produces a precursor that is about 100 nucleotides longer than the mature RNA with all the extra nucleotides at the 3' end. The gene contains an open reading frame that corresponds to a small protein 25 amino acids long. ..
  34. Barends S, Björk K, Gultyaev A, de Smit M, Pleij C, Kraal B. Functional evidence for D- and T-loop interactions in tmRNA. FEBS Lett. 2002;514:78-83 pubmed
    ..Strikingly, this in evolution conserved interaction is not primarily important for tmRNA alanylation and for binding to elongation factor Tu, but especially for a proper functioning of SmpB. ..
  35. Williams K. The tmRNA website. Nucleic Acids Res. 2000;28:168 pubmed
    ..Updates are very frequent. The tmRNA Website has a new URL: ..
  36. Tanner D, Dewey J, Miller M, Buskirk A. Genetic analysis of the structure and function of transfer messenger RNA pseudoknot 1. J Biol Chem. 2006;281:10561-6 pubmed
    ..Such mutations may only destabilize a global fold that could be formed equally well by an entirely different, stable structure. ..
  37. Hersch G, Baker T, Sauer R. SspB delivery of substrates for ClpXP proteolysis probed by the design of improved degradation tags. Proc Natl Acad Sci U S A. 2004;101:12136-41 pubmed
    The ssrA-degradation tag sequence contains contiguous binding sites for the SspB adaptor and the ClpX component of the ClpXP protease...
  38. Felden B, Himeno H, Muto A, McCutcheon J, Atkins J, Gesteland R. Probing the structure of the Escherichia coli 10Sa RNA (tmRNA). RNA. 1997;3:89-103 pubmed
    ..Several discrepancies between the probing data and the phylogeny suggest that E. coli tmRNA undergoes a conformational change. ..
  39. O Connor M. Minimal translation of the tmRNA tag-coding region is required for ribosome release. Biochem Biophys Res Commun. 2007;357:276-81 pubmed
    ..These results suggest that the main function of tmRNA in releasing stalled ribosomes is to supply a stop codon and so facilitate termination and subsequent ribosome recycling. ..
  40. Tu G, Reid G, Zhang J, Moritz R, Simpson R. C-terminal extension of truncated recombinant proteins in Escherichia coli with a 10Sa RNA decapeptide. J Biol Chem. 1995;270:9322-6 pubmed
    ..A mutant strain of E. coli in which the chromosomal 10Sa RNA gene (ssrA) is disrupted does not produce this C-terminal modification, confirming that the tag peptide originates from the ..
  41. Dougan D, Weber Ban E, Bukau B. Targeted delivery of an ssrA-tagged substrate by the adaptor protein SspB to its cognate AAA+ protein ClpX. Mol Cell. 2003;12:373-80 pubmed
    In the bacterial cytosol, degradation of ssrA-tagged proteins is primarily carried out by the proteolytic machine ClpXP in a process which is stimulated by a ClpX-specific adaptor protein, SspB...
  42. Miczak A, Chauhan A, Apirion D. Two new genes located between 2758 and 2761 kilobase pairs on the Escherichia coli genome. J Bacteriol. 1991;173:3271-2 pubmed
  43. Burton R, Baker T, Sauer R. Energy-dependent degradation: Linkage between ClpX-catalyzed nucleotide hydrolysis and protein-substrate processing. Protein Sci. 2003;12:893-902 pubmed
    ..of ATP and ATPgammaS by ClpX were measured with different protein partners and the kinetics of degradation of ssrA-tagged substrates were determined with both nucleotides...
  44. Himeno H, Ushida C, Muto A. [tmRNA: a novel RNA molecule possessing a dual function as a tRNA and as an mRNA]. Seikagaku. 1997;69:1204-8 pubmed
  45. Spiers A, Lamb H, Cocklin S, Wheeler K, Budworth J, Dodds A, et al. PDZ domains facilitate binding of high temperature requirement protease A (HtrA) and tail-specific protease (Tsp) to heterologous substrates through recognition of the small stable RNA A (ssrA)-encoded peptide. J Biol Chem. 2002;277:39443-9 pubmed
    ..E. coli has a system of protein quality control surveillance mediated by the ssrA-encoded peptide tagging system...
  46. DeLisa M, Samuelson P, Palmer T, Georgiou G. Genetic analysis of the twin arginine translocator secretion pathway in bacteria. J Biol Chem. 2002;277:29825-31 pubmed
    ..Specifically, export via the Tat pathway rescues green fluorescent protein (GFP) fused to an SsrA peptide from degradation by the cytoplasmic proteolytic ClpXP machinery...
  47. Rudinger Thirion J, Giege R, Felden B. Aminoacylated tmRNA from Escherichia coli interacts with prokaryotic elongation factor Tu. RNA. 1999;5:989-92 pubmed
  48. Janssen B, Hayes C. Kinetics of paused ribosome recycling in Escherichia coli. J Mol Biol. 2009;394:251-67 pubmed publisher
    ..Peptidyl-tRNA turnover from nonstop-paused ribosomes in DeltatmRNA cells suggests the existence of another uncharacterized ribosome rescue pathway. ..
  49. Bordeau V, Felden B. Ribosomal protein S1 induces a conformational change of tmRNA; more than one protein S1 per molecule of tmRNA. Biochimie. 2002;84:723-9 pubmed
    tmRNA (10Sa RNA, ssrA) acts to rescue stalled bacterial ribosomes while encoding a peptide tag added trans-translationally to the nascent peptide, targeting it for proteolysis...
  50. Collier J, Bohn C, Bouloc P. SsrA tagging of Escherichia coli SecM at its translation arrest sequence. J Biol Chem. 2004;279:54193-201 pubmed
    ..We report that secretion deficiencies lead to SsrA tagging of SecM after Pro(166), Gly(165), and likely Arg(163)...
  51. Herman C, Thevenet D, Bouloc P, Walker G, D Ari R. Degradation of carboxy-terminal-tagged cytoplasmic proteins by the Escherichia coli protease HflB (FtsH). Genes Dev. 1998;12:1348-55 pubmed
    ..Such proteins are tagged with an 11-amino-acid nonpolar destabilizing tail via a mechanism involving the 10Sa (SsrA) stable RNA and then degraded...
  52. Wah D, Levchenko I, Rieckhof G, Bolon D, Baker T, Sauer R. Flexible linkers leash the substrate binding domain of SspB to a peptide module that stabilizes delivery complexes with the AAA+ ClpXP protease. Mol Cell. 2003;12:355-63 pubmed
    SspB dimers bind proteins bearing the ssrA-degradation tag and stimulate their degradation by the ClpXP protease. Here, E...
  53. Bugaeva E, Shpanchenko O, Felden B, Isaksson L, Dontsova O. One SmpB molecule accompanies tmRNA during its passage through the ribosomes. FEBS Lett. 2008;582:1532-6 pubmed publisher
    ..Ribosome, tmRNA and SmpB were found in equimolar amount in the tmRNA-ribosome complexes stopped at the position of the 2nd, 4th, 5th or the 11th codons of the coding part of the tmRNA. ..
  54. Dulebohn D, Cho H, Karzai A. Role of conserved surface amino acids in binding of SmpB protein to SsrA RNA. J Biol Chem. 2006;281:28536-45 pubmed
    ..A complex of SmpB protein and SsrA RNA orchestrates this salvage process...
  55. Munavar H, Zhou Y, Gottesman S. Analysis of the Escherichia coli Alp phenotype: heat shock induction in ssrA mutants. J Bacteriol. 2005;187:4739-51 pubmed
    ..Inactivation of transfer mRNA (tmRNA) (encoded by ssrA), coupled with a multicopy kanamycin resistance determinant, suppressed both lon phenotypes and restored the rapid ..
  56. Bolon D, Grant R, Baker T, Sauer R. Nucleotide-dependent substrate handoff from the SspB adaptor to the AAA+ ClpXP protease. Mol Cell. 2004;16:343-50 pubmed publisher
    The SspB adaptor enhances ClpXP degradation by binding the ssrA degradation tag of substrates and the AAA+ ClpX unfoldase...
  57. O Handley D, Nakai H. Derepression of bacteriophage mu transposition functions by truncated forms of the immunity repressor. J Mol Biol. 2002;322:311-24 pubmed
    ..Such peptides with a C-terminal ssrA degradation tag promoted a sharp reduction in cellular levels of full-length unmodified repressor, a process ..
  58. Atkins J, Gesteland R. A case for trans translation. Nature. 1996;379:769-71 pubmed
  59. Gillet R, Felden B. Emerging views on tmRNA-mediated protein tagging and ribosome rescue. Mol Microbiol. 2001;42:879-85 pubmed
    Transfer-messenger RNA (tmRNA), also known as SsrA or 10Sa RNA, is a bacterial ribonucleic acid that recycles 70S ribosomes stalled on problematic messenger RNAs (mRNAs) and also contributes to the degradation of incompletely synthesized ..
  60. Wower J, Zwieb C. The tmRNA database (tmRDB). Nucleic Acids Res. 1999;27:167 pubmed
    ..The data are available freely at the URL +html ..
  61. Retallack D, Friedman D. A role for a small stable RNA in modulating the activity of DNA-binding proteins. Cell. 1995;83:227-35 pubmed
    The 10Sa RNA, encoded by the E. coli ssrA gene, appears to modulate action of some DNA-binding proteins...
  62. Park E, Song H. A degradation signal recognition in prokaryotes. J Synchrotron Radiat. 2008;15:246-9 pubmed publisher
    The degradation of ssrA-tagged substrates in prokaryotes is conducted by a subset of ATP-dependent proteases, including ClpXP complex...
  63. Gaudin C, Nonin Lecomte S, Tisne C, Corvaisier S, Bordeau V, Dardel F, et al. The tRNA-like domains of E coli and A.aeolicus transfer-messenger RNA: structural and functional studies. J Mol Biol. 2003;331:457-71 pubmed
    Transfer-messenger RNA (tmRNA, 10Sa RNA or ssrA) acts to rescue stalled bacterial ribosomes while encoding a peptide tag added trans-translationally to the nascent peptide, targeting it for proteolysis...