Cue2 and Slh1 define parallel pathways to rescue stalled ribosomes

Ribosome stalling at problematic sequences in mRNAs leads to collisions that trigger a collection of quality control events including ribosome rescue, targeting the nascent polypeptide for decay (Ribosome-mediated Quality Control or RQC), and targeting of the mRNA for decay (No Go Decay or NGD). Using a reverse genetic screen in yeast, we identify Cue2 as the endonuclease that is recruited to stalled ribosomes to promote NGD. Following Cue2-mediated cleavage, ribosomes upstream of the cleavage site translate to the end of the truncated mRNA and are rescued by the Dom34:Hbs1 complex. We also show that the putative helicase Slh1 (part of the RQC Trigger or RQT complex) removes collided ribosomes behind the lead stalled ribosome and thereby reduces endonucleolytic cleavage by Cue2. The synergistic activities of Cue2 and Slh1 define two parallel pathways that allow cells to recognize and respond to ribosomes trapped on problematic mRNAs. Overall design: 7 samples for ribosome profiling experiments using various yeast strains and 3 samples for in vitro ribosome footprinting experiments using isloated trisomes from sucrose gradients.