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Symposium: Translational Control: A Mechanistic Perspective

Quality Control of the Elongation Step of Protein Synthesis by tmRNP^{1 ,2}

Jacek Wower^*,3, Iwona K. Wower^*, Barend Kraal and Christian W. Zwieb^**

Department of Animal and Dairy Sciences, Program in Cell and Molecular Biosciences, Auburn University, Auburn, AL 36849-5415; Department of Biochemistry, Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands; and Department of Molecular Biology, The University of Texas Health Science Center at Tyler, 11937 US Highway 271, Tyler, TX 75708-3154 . ^{** *}

³To whom correspondence should be addressed. E-mail: jwower{at}acesag.auburn.edu

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.

KEY WORDS: • 10Sa RNA • SsrA RNA • tmRNA • trans-translation • peptide tagging