Tittel, L. S. | bioRxiv Science

bioRxiv2025

Jlp2 is an RQC complex-independent release factor acting on aberrant peptidyl-tRNA, protecting cells against translation elongation stress

Ribosome stalling generates aberrant nascent peptides that remain tethered to the large ribosomal subunit following ribosome splitting. Such peptidyl tRNA:60S complexes are processed by the Ribosome associated Quality Control (RQC) pathway, where Ltn1 and Rqc1 mediate K48 linked ubiquitination and Rqc2 adds CAT tails to the nascent peptides.Subsequently, Vms1 releases the peptides from tRNA, enabling their proteasomal degradation. However, alternative mechanisms that process these stalled intermediates remain poorly defined. In this study, we identify Jlp2 as a novel factor involved in translation quality control. We find that Jlp2 is a release factor that catalyzes peptide release from tRNA and suppresses excessive CAT tailing when Ltn1-dependent ubiquitination is compromised. We define its ribosome binding properties, substrate scope, and critical residues required for peptide release. Our data support a model in which Jlp2-mediated peptide release constitutes an alternative quality control mechanism to safeguard cells during ribosome stalling and conditions of RQC failure or insufficiency.

molecular biology↗

bioRxiv2024

Yeast elongation factor homolog New1 protects a subset of mRNAs from degradation by no-go decay

New1 is a homologue of the essential yeast translation elongation factor eEF3. Lack of New1 has previously been shown to induce queueing of ribosomes upstream of the stop codon on mRNAs encoding specific C-terminal amino acids, primarily lysine and arginine. Here, we used UV crosslinking and analysis of cDNA, long-read nanopore sequencing and proteomics to address the open question of what consequences such queues have for the yeast cell. We show that these queues are ribosomal collisions, which are recognized by the collision sensor and E3 ubiquitin ligase Hel2, marking these collided ribosome complexes for mRNA degradation via canonical no-go decay. Decay is initiated by Cue2-mediated cleavage upstream of the stop codon. Ultimately, this leads to downregulation of encoded proteins, including highly abundant and important metabolic enzymes Pgk1 and Gpm1, as well as translation elongation factors eEF1-alpha and eEF1-beta. Collisions and resulting downstream effects are codon-, rather than amino acid dependent. E.g., for C-terminal lysine and arginine, only specific codons induce collisions upon lack of New1. Our study shows that New1 protects highly abundant and essential genes from degradation by no-go decay thatwould otherwise occur in the absence of translation inhibitors or other direct perturbations of translation.

molecular biology↗