Ribosome quality control complex subunit 2

UniProtKB accession:  Q12532

Grouped By:  Matching UniProtKB accession

UniProtKB description:  Key component of the ribosome quality control complex (RQC), a ribosome-associated complex that mediates the extraction of incompletely synthesized nascent chains from stalled ribosomes as well as their ubiquitin-mediated proteasomal degradation (PubMed:20691087, PubMed:23178123, PubMed:23479637, PubMed:25349383, PubMed:25554787, PubMed:26934223, PubMed:28751611, PubMed:32934225). Thereby, frees 60S subunit ribosomes from the stalled translation complex and prevents the accumulation of nascent polypeptide chains that are potentially toxic for the cell (PubMed:23178123). Within the RQC complex, RQC2 specifically binds stalled 60S ribosomal subunits by recognizing an exposed, nascent chain-conjugated tRNA moiety and promotes the recruitment of RKR1/LTN1 to stalled 60S subunits (PubMed:23479637, PubMed:25349383). Following binding to stalled 60S ribosomal subunits, RQC2 mediates CAT tailing by recruiting alanine- and threonine-charged tRNA to the A-site and directing the elongation of stalled nascent chains independently of mRNA or 40S subunits, leading to non-templated C-terminal Ala and Thr extensions (CAT tails) (PubMed:25554787, PubMed:27129255, PubMed:26934223, PubMed:28751611, PubMed:32934225, PubMed:36804914). CAT tails promote the RKR1/LTN1-mediated ubiquitination of incompletely synthesized nascent polypeptides: CAT tailing facilitates RKR1/LTN1-dependent ubiquitination by exposing lysine residues that would otherwise remain buried in the ribosomal exit tunnel (PubMed:32934225, PubMed:28751611). Following ubiquitination, incompletely synthesized nascent polypeptides are recognized by CDC48 and degraded by the proteasome (PubMed:27129255). CAT-tailed proteins tend to aggregate and sequester chaperones and can induce proteotoxic stress; their RKR1/LTN1-dependent ubiquitination and degradation is required to prevent proteotoxic stress (PubMed:27129255, PubMed:26934223, PubMed:31133701).