Fidelity in gene expression is maintained by a variety of mechanisms, including monitoring of mRNA templates and protein products. Although faulty mRNAs and the deviant polypeptides produced from them are usually subjected to accelerated degradation, ribosomes engaged in aberrant translation are probably recycled. Impediments that block ribosome translocation result in dissociation of the 40S ribosomal subunit and recruitment of the ribosome quality-control complex (RQC) to the peptide-bound 60S complex. The RQC guides tagging of the peptide for degradation via the Ltn1 E3 ligase and presumably mediates the release of the ribosomal subunit for reuse. Recent cryo-EM and functional studies by Weissman, Brandman, Frost and colleagues have uncovered a previously undefined role for the RQC component Rqc2 in mediating extension of nascent peptides in a template-independent manner. In the presence of an E3-deficient Ltn1 mutant, the authors were able to capture Rqc2-bound 60S subunits with nascent peptide chains in the ribosome exit tunnel. Rqc2 was located on the 40S-binding surface and appeared to associate with the peptidyl- and aminoacyl-site tRNAs, which were enriched for alanyl and threonyl tRNAs. Previous studies had shown the presence of extended polypeptides in an ltn1Δ strain. Here, the authors biochemically identified these extensions as Rqc2-dependent C-terminal 'CAT' tails comprising alanine and threonine residues. Interestingly, these CAT tails were required for the induction of a heat shock factor 1–dependent transcriptional response, which had previously been observed to occur upon the accumulation of stalled peptides in an Rqc2-dependent manner. In summary, Rqc2's ability to direct polypeptide chain extension provides a general mechanism whereby stalled nascent polypeptides can be marked in a sequence-independent manner. (Science 347, 75–78, 2015)