Sense codon-misassociated eRF1 elicits widespread ribosome stalling subjected to quality control

The ribosome-associated quality control (RQC) is a surveillance system for aberrant translation, sensing ribosome collisions. Although the molecular mechanism has been extensively studied, the endogenous targets of RQC in human cells were poorly understood. Here, starting from the study of codon specificity of eukaryotic termination factor eRF1, we unexpectedly find that misrecognition of UUA sense codon by eRF1 leads to ribosome collisions and provides the source of RQC substrates in humans. eRF1-selective Monosome-Seq and Disome-Seq reveal that eRF1 recruitment to ribosome was not restricted to the stop codons but also the sub-cognate sense codons, including the UUA codon. The UUA misrecognition by eRF1 causes ribosome collision without termination reaction. Remarkably, Disome-Seq with the depletion of ASCC3 and 4EHP, key factors in RQC, showed that ribosome stalled at UUA codons are the predominant sub-populations rescued by RQC. Failure to resolve ribosome collisions by RQC triggers p38 phosphorylation and upregulation of stress response transcription factor ATF3. This study presents the impact of sense codon misrecognition by the termination factor on translation homeostasis in human cells.