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tmRNA to the rescue: Structural motives for the salvage of stalled ribosomes

Volume 7, Issue 5   September/October 2010
Pages 577 - 581
http://dx.doi.org/10.4161/rna.7.5.13214
Authors: Martin Lindahl

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Abstract:

During translation, mRNA molecules are incidentally damaged, leaving the ribosome unable to reach or recognize the stop codon and thus stalled with mRNA and a potentially harmful polypeptide product attached to tRNA in the ribosomal P-site. In bacteria, a process called trans-translation has evolved, where a protein-RNA complex (smpB-tmRNA) mimicks the role of aminoacyl charged tRNA, replacing stalled tRNA in the ribosomal A-site. The ribosome then resumes protein synthesis guided by an mRNA-like portion of the tmRNA which ends with a stop codon, and codes for a peptide sequence susceptible to proteolysis, thus allowing the bacteria to salvage stalled ribosomes and degrade ill-defined and potentially harmful protein products. In this article, we will recollect how structural studies have yielded a model for how the pre-translocation stages of trans-translation employing structural mimicry. We will also discuss possible models for how the translocation may be carried out.

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