Recycling of aborted ribosomal 50S subunit-nascent chain-tRNA complexes by the heat shock protein Hsp15.
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.
Jiang
Linhua
L
Department of Biophysical Structural Chemistry, Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands.
Schaffitzel
Christiane
C
Bingel-Erlenmeyer
Rouven
R
Ban
Nenad
N
Korber
Philipp
P
Koning
Roman I
RI
de Geus
Daniël C
DC
Plaisier
Jasper R
JR
Abrahams
Jan Pieter
JP
D020285:Cryoelectron Microscopy; D004268:DNA-Binding Proteins / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D006360:Heat-Shock Proteins / Q000737:chemistry*; D008958:Models, Molecular; D011691:Puromycin / Q000737:chemistry; D012329:RNA, Bacterial / Q000737:chemistry*; D012343:RNA, Transfer / Q000737:chemistry*; D054681:Ribosome Subunits, Large, Bacterial / Q000737:chemistry*
D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D012329:RNA, Bacterial; C116841:hslR protein, E coli; D011691:Puromycin; D012343:RNA, Transfer