Structural Basis for the Rescue of Stalled Ribosomes: Structure of YaeJ Bound to the Ribosome

Abstract

Ribosome Rescue Ribosomes stall when they reach the end of defective messenger RNAs (mRNAs). In bacteria, the most-studied ribosomal rescue pathway involves a ribonucleoprotein complex comprising tmRNA (which acts as both transfer RNA and mRNA) and the protein SmpB. In an alternative pathway, some Gram-negative bacteria contain proteins that achieve tmRNA-independent rescue. Now, Neubauer et al. (p. 1366 ) present the structure of the Thermus thermophilus ribosome bound to a fragment of tmRNA, SmpB, and elongation factor Tu, and Gagnon et al. (p. 1370 ) report the structure of the T. thermophilus ribosome in complex with an initiator tRNA, a short mRNA fragment, and the rescue factor YaeJ. Though the two rescue systems are very different, both involve a protein tail that binds in the mRNA channel. This orients the rescue apparatus to facilitate switching translation to a different message in the tmRNA system or hydrolysis of peptidyl tRNA by YaeJ.