title: The ribosome quality control pathway can access nascent polypeptides stalled at the Sec61 translocon.
abstract: Cytosolic ribosomes that stall during translation are split into subunits, and nascent polypeptides trapped in the 60S subunit are ubiquitinated by the ribosome quality control (RQC) pathway. Whether the RQC pathway can also target stalls during cotranslational translocation into the ER is not known. Here we report that listerin and NEMF, core RQC components, are bound to translocon-engaged 60S subunits on native ER membranes. RQC recruitment to the ER in cultured cells is stimulated by translation stalling. Biochemical analyses demonstrated that translocon-targeted nascent polypeptides that subsequently stall are polyubiquitinated in 60S complexes. Ubiquitination at the translocon requires cytosolic exposure of the polypeptide at the ribosome-Sec61 junction. This exposure can result from either failed insertion into the Sec61 channel or partial backsliding of translocating nascent chains. Only Sec61-engaged nascent chains early in their biogenesis were relatively refractory to ubiquitination. Modeling based on recent 60S-RQC and 80S-Sec61 structures suggests that the E3 ligase listerin accesses nascent polypeptides via a gap in the ribosome-translocon junction near the Sec61 lateral gate. Thus the RQC pathway can target stalled translocation intermediates for degradation from the Sec61 channel.
authors: MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
authors: Karina
authors: K
authors: von der Malsburg
authors: MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
authors: Sichen
authors: S
authors: Shao
authors: MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom rhegde@mrc-lmb.cam.ac.uk.
authors: Ramanujan S
authors: RS
authors: Hegde
mesh_terms: D018870:Endoplasmic Reticulum, Rough / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D008958:Models, Molecular; D010441:Peptide Chain Elongation, Translational; D010455:Peptides / Q000378:metabolism*; D021381:Protein Transport; D054683:Ribosome Subunits, Large, Eukaryotic / Q000378:metabolism*; D000069816:SEC Translocation Channels; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D008565:Membrane Proteins; D010455:Peptides; D000069816:SEC Translocation Channels; C000607499:LTN1 protein, human; D044767:Ubiquitin-Protein Ligases