Poster Sessions

Mol-18

Mee-Ngan Yap

M. N. Yap, H. Bernstein

Nascent polypeptide-mediated translational regulation inside the ribosome tunnel

Under certain physiological conditions, the recognition of a 17 residue segment of the E. coli SecM protein inside the ribosome tunnel causes translation arrest. Here we describe the characterization of novel translation arrest motifs isolated in a genetic screen and divergent SecM homologs that we found to be completely functional in E. coli. The data indicate that many different functional motifs can be created through extensive remodeling of the E. coli SecM translation arrest peptide. We found that while only two residues, R163 and P166, are essential for translation arrest, flanking residues that vary both in position and number also play an important secondary role. Furthermore, we found that mutations in the ribosome tunnel produce variable effects on the activity of individual translation arrest motifs. To account for our results, we propose that nascent polypeptides adopt sequence-dependent conformations inside the ribosome tunnel, and that translation arrest occurs only when the conformation places R163 into a precise location. Our data provide evidence for a complex interaction between the ribosome tunnel and nascent polypeptides and may help to explain the striking diversity of peptides that cause translation arrest in prokaryotes and eukaryotes.