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tmRNA regulates synthesis of the ArfA ribosome rescue factor.
Mol Microbiol. 2011 Jun; 80(5):1204-19
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01 Jun 2011
New Finding
DOI: 10.3410/f.10867956.11787054
I found this article interesting because it describes the first protein that is physiologically encoded by a non-stop mRNA lacking a stop codon.
The arfA gene product, together with the trans-translation system, participates in rescuing the ribosome stalled at the end of non-stop mRNAs in E. coli (see my F1000 evaluation of a recent article by Chadani et al. {1,2}). In the present work, the authors show that the arfA mRNA is cleaved by RNase III within its coding sequence, producing a truncated mRNA. Therefore, its protein product is usually down-regulated by a trans-translation-mediated attachment of the SsrA-degradation tag to the C-terminus of the incomplete polypeptide. When activity of the trans-translation system is compromised, the truncated ArfA protein is produced at least initially in a form of peptidyl-tRNA. The ArfA incomplete polypeptide then functions as the alternative ribosome-rescuing factor by binding to the ribosomes and inducing peptidyl-tRNA hydrolysis.
References
1.
Ribosome rescue by Escherichia coli ArfA (YhdL) in the absence of trans-translation system.
Mol Microbiol. 2010; 78: 796-808
PMID: 21062370
DOI: 10.1111/j.1365-2958.2010.07375.x
2.
F1000 evaluation of: Chadani Y et al. Ribosome rescue by Escherichia coli ArfA (YhdL) in the absence of trans-translation system. Mol Microbiol 2010 Nov; 78(4):796-808; doi:10.1111/j.1365-2958.2010.07375.x, PMID:21062370
Faculty of 1000, 01 Nov 2010
Disclosures
None declared
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Ito K: F1000Prime Recommendation of [Garza-Sánchez F et al., Mol Microbiol 2011, 80(5):1204-19]. In F1000Prime, 01 Jun 2011; DOI: 10.3410/f.10867956.11787054. F1000Prime.com/10867956#eval11787054
F1000Prime Recommendations, Dissents and Comments for [Garza-Sánchez F et al., Mol Microbiol 2011, 80(5):1204-19]. In F1000Prime, 20 Jun 2013; F1000Prime.com/10867956
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Translation of mRNA lacking an in-frame stop codon leads to ribosome arrest at the 3' end of the transcript. In bacteria, the tmRNA quality control system recycles these stalled ribosomes and tags the incomplete nascent chains for degradation. Although ubiquitous in eubacteria, the ssrA gene encoding tmRNA is not essential for the viability of Escherichia coli and other model bacterial species. ArfA (YhdL) is a mediator of tmRNA-independent ribosome rescue that is essential for the viability of E. coliΔssrA mutants. Here, we demonstrate that ArfA is synthesized from truncated mRNA and therefore regulated by tmRNA tagging activity. RNase III cleaves a hairpin structure within the arfA-coding sequence to produce transcripts that lack stop codons. In the absence of tmRNA tagging, truncated ArfA chains are released from the ribosome. The truncated ArfAΔ18 protein (which lacks 18 C-terminal residues) is functional in ribosome rescue and supports ΔssrA cell viability when expressed from the arfA locus. Other proteobacterial arfA genes also encode hairpins, and transcripts from Dickeya dadantii and Salmonella typhimurium are cleaved by RNase III when expressed in E. coli. Thus, synthesis of ArfA from truncated mRNA appears to be a general mechanism to regulate alternative ribosome rescue activity.
© 2011 Blackwell Publishing Ltd.
DOI: 10.1111/j.1365-2958.2011.07638.x
PMID: 21435036
