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Decoding in the Absence of a Codon by tmRNA and SmpB in the Ribosome

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Science  16 Mar 2012:
Vol. 335, Issue 6074, pp. 1366-1369
DOI: 10.1126/science.1217039

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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.

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