Recycling of aborted ribosomal 50S subunit-nascent chain-tRNA complexes by the heat shock protein Hsp15

J Mol Biol. 2009 Mar 13;386(5):1357-67. doi: 10.1016/j.jmb.2008.10.079. Epub 2008 Nov 5.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cryoelectron Microscopy
  • DNA-Binding Proteins / chemistry*
  • Escherichia coli Proteins / chemistry*
  • Heat-Shock Proteins / chemistry*
  • Models, Molecular*
  • Puromycin / chemistry
  • RNA, Bacterial / chemistry*
  • RNA, Transfer / chemistry*
  • Ribosome Subunits, Large, Bacterial / chemistry*

Substances

  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • Heat-Shock Proteins
  • RNA, Bacterial
  • hslR protein, E coli
  • Puromycin
  • RNA, Transfer

Associated data

  • PDB/3BBU
  • PDB/3BBV
  • PDB/3BBX