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Elsevier, Journal of Molecular Biology, 5(386), p. 1357-1367, 2009

DOI: 10.1016/j.jmb.2008.10.079

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Recycling of Aborted Ribosomal 50S Subunit-Nascent Chain-tRNA Complexes by the Heat Shock Protein Hsp15

This paper is available in a repository.
This paper is available in a repository.

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Abstract

When heat shock prematurely dissociates a translating bacterial ribosome, its 50S subunit is prevented from reinitiating protein synthesis by tRNA covalently linked to the unfinished protein chain that remains threaded through the exit tunnel. Hsp15, a highly upregulated bacterial heat shock protein, reactivates such dead-end complexes. Here, we show with cryo-electron microscopy reconstructions and functional assays that Hsp15 translocates the tRNA moiety from the A site to the P site of stalled 50S subunits. By stabilizing the tRNA in the P site, Hsp15 indirectly frees up the A site, allowing a release factor to land there and cleave off the tRNA. Such a release factor must be stop codon independent, suggesting a possible role for a poorly characterized class of putative release factors that are upregulated by cellular stress, lack a codon recognition domain and are conserved in eukaryotes.