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 (RQC) system. Here we report that ubiquitination of the 40S ribosomal protein uS10 by the E3 ubiquitin ligase Hel2 (or RQT1) is required for RQC. We identify a RQC-trigger (RQT) subcomplex composed of the RNA helicase-family protein Slh1/Rqt2, the ubiquitin-binding protein Cue3/Rqt3, and yKR023W/Rqt4 that is required for RQC. The defects in RQC of the RQT 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 RQC substrates. Rqt1 specifically ubiquitinates these arrested ribosomes to target them to the RQT complex, allowing subsequent RQC reactions including dissociation of the stalled ribosome into subunits

Sequential Ubiquitination of Ribosomal Protein uS3 Triggers the Degradation of Non-functional 18S rRNA

Summary: 18S non-functional rRNA decay (NRD) eliminates non-functional 18S rRNA with deleterious mutations in the decoding center. Dissociation of the non-functional 80S ribosome into 40S and 60S subunits is a prerequisite step for degradation of the non-functional 18S rRNA. However, the mechanisms by which the non-functional ribosome is recognized and dissociated into subunits remain elusive. Here, we report that the sequential ubiquitination of non-functional ribosomes is crucial for subunit dissociation. 18S NRD requires Mag2-mediated monoubiquitination followed by Hel2- and Rsp5-mediated K63-linked polyubiquitination of uS3 at the 212th lysine residue. Determination of the aberrant 18S rRNA levels in sucrose gradient fractions revealed that the subunit dissociation of stalled ribosomes requires sequential ubiquitination of uS3 by E3 ligases and ATPase activity of Slh1 (Rqt2), as well as Asc1 and Dom34. We propose that sequential uS3 ubiquitination of the non-functional 80S ribosome induces subunit dissociation by Slh1, leading to degradation of the non-functional 18S rRNA. : 18S non-functional rRNA decay (NRD) eliminates non-functional 18S rRNA with deleterious mutations in the decoding center. Sugiyama et al. show that 18S NRD requires Mag2-mediated monoubiquitination followed by Hel2- and Rsp5-mediated K63-linked polyubiquitination of uS3. Subunit dissociation requires Asc1, Dom34, sequential ubiquitination of uS3, and ATPase activity of Slh1 (Rqt2). Keywords: non-functional rRNA decay, ribosome ubiquitination, sequential ubiquitination, RQT complex, subunit dissociatio

Catalytic Desymmetrization of Cyclohexadienes by Asymmetric Bromolactonization

Asymmetric bromolactonization of prochiral cyclohexadiene derivatives with <i>N</i>-bromosuccimide proceeded in the presence of (DHQD)₂PHAL as a chiral catalyst to afford the corresponding bromolactones with up to 93% ee. This reaction was also applicable to the kinetic resolution of a racemic cyclic ene-carboxylic acid, where the starting material was recovered with high enantioselectivity

Practical synthesis of natural plant-growth regulator 2-azahypoxanthine, its derivatives, and biotin-labeled probes

autho