Ubiquitination of stalled ribosome triggers ribosome-associated quality control.

Translation arrest by polybasic sequences induces ribosome stalling, and the arrest product is degraded by the ribosome-mediated quality control system. Here we report that ubiquitination of the 40S ribosomal protein uS10 by the E3 ubiquitin ligase Hel2 (or is required for We identify a subcomplex composed of the RNA helicase-family protein Slh1/Rqt2, the ubiquitin-binding protein Cue3/Rqt3, and yKR023W/Rqt4 that is required for duanyu1745C. The defects in of the mutants correlate with sensitivity to anisomycin, which stalls ribosome at the rotated form. Cryo-electron microscopy analysis reveals that Hel2-bound ribosome are dominantly the rotated form with hybrid tRNAs. Ribosome profiling reveals that ribosomes stalled at the rotated state with specific pairs of codons at P-A sites serve as duanyu1745C substrates. Rqt1 specifically ubiquitinates these arrested ribosomes to target them to the duanyu1745T complex, allowing subsequent duanyu1745C reactions including dissociation of the stalled ribosome into subunits.Several protein quality control mechanisms are in place to trigger the rapid degradation of aberrant polypeptides and mRNAs. Here the authors describe a mechanism of ribosome-mediated quality control that involves the ubiquitination of ribosomal proteins by the E3 ubiquitin ligase

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