Talk on Saturday 10:06-10:18am submitted by Heather Feaga
Ribosome release from non-stop mRNAs is essential
Heather A. Feaga (Department of Biochemistry and Molecular Microbiology, Pennsylvania State University), Kenneth C. Keiler (Department of Biochemistry and Molecular Microbiology, Pennsylvania State University)
Messenger RNAs frequently lack a stop codon due to RNase activity or aberrant transcription. In bacteria, when the ribosome initiates transcription on one of these non-stop RNAs, it cannot be released by classical termination factors. All bacteria have an RNA-based solution to this challenge- tmRNA- a molecule that has the activity of both a tRNA and an mRNA. tmRNA enters the A-site of the stalled ribosome and accepts the nascent polypeptide. The ribosome then resumes translation on the reading frame encoded by the mRNA-like portion of tmRNA. It is estimated that about 2-4% of all translation events end in tmRNA mediated release. Surprisingly, some species of bacteria, such as Caulobacter crescentus, can survive when tmRNA is deleted. Using a synthetic-lethal screen, we identified a back up system for tmRNA. ArfBCc can hydrolyze peptidly-tRNA translated from non-stop mRNA in vitro. Homologs are present in the majority of bacteria phyla, but are absent in species where tmRNA deletion has proved lethal. These data suggest that release of non-stop ribosomes may be essential in all bacteria.
Keywords: tmRNA, ArfB, ribosome release