Quality control of the elongation step of protein synthesis by tmRNP.
Trans-translation is a quality-control process, activated upon premature termination of protein elongation, which recycles stalled ribosomes and degrades incomplete polypeptides. These functions are facilitated by transfer-messenger RNA (tmRNA, also called 10Sa RNA or SsrA RNA), a small stable RNA molecule encoded by the SsrA gene found in bacteria, chloroplasts and mitochondria. Most tmRNAs consist of a tRNA- and an mRNA-like domain connected by up to four pseudoknots. Comparative sequence analysis provided the first insight into tmRNA secondary and three-dimensional structure. Studies of the E. coli tmRNA in vitro and in vivo demonstrated that tmRNA functions as a ribonucleoprotein (RNP) complex with elongation factor Tu (EF-Tu), protein SmpB and ribosomal protein S1. The tRNA-like and mRNA-like activities of tmRNA mark prematurely terminated proteins for degradation by attaching to their C-termini peptide tags, which are recognized by numerous proteases. Studies aimed at understanding the details of the molecular mechanisms of trans-translation are ongoing.
Wower
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Department of Animal and Dairy Sciences, Program in Cell and Molecular Biosciences, Auburn University, Auburn, AL 36849-5415, USA. jwower@acesag.auburn.edu
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D010445:Peptide Elongation Factors / Q000502:physiology*; D014176:Protein Biosynthesis; D011786:Quality Control; D012329:RNA, Bacterial / Q000502:physiology*; D017421:Sequence Analysis
D010445:Peptide Elongation Factors; D012329:RNA, Bacterial; C096222:tmRNA