tmRNA (also known as 10Sa RNA) is so-named for its dual tRNA-like and mRNA-like nature. It is employed in a remarkable trans-translation process to add a Cterminal peptide tag to the incomplete protein product of a broken mRNA; the tag targets the abnormal protein for proteolysis. tmRNA sequences have been identified in genomes of diverse bacterial phyla, including the most deeply branching. They have also been identified in plastids of the `red' lineage. The tmRNA Website (http://www.wi.mit.edu/bartel/tmRNA/ home ) contains a database currently including sequences from 37 species, with provisional alignments, as well as the tentatively predicted proteolysis tag sequences. A brief review and guide to the literature is also provided. tmRNA STRUCTURE AND FUNCTION The bacterial RNA with the provisional biochemical designation 10Sa (1,2) was renamed tmRNA (3,4) when its combined tRNA-like and mRNA-like properties were recognized. A half-tRNA structure, with a coaxially stacked T stem
Kelly P. Williams