Ubiquitin and the Control of Translation During Oxidative Stress.

During exposure to environmental stresses, eukaryotic cells must reprogram gene expression at the transcriptional and translational levels in order to thrive under these new conditions. Dysregulation of gene expression under stress can lead to molecular damage, cellular death, and the progression of diseases. Therefore, regulation of gene expression is dynamic, requires multiple layers of control, and is critical for cellular adaptation and survival. However, many of these control mechanisms, particularly at the translational level, remain elusive. In response to oxidative stress, we observed in budding yeast a massive accumulation of K63 ubiquitin conjugates that supports cellular resistance to stress. By developing a sequential enrichment methodology, our proteomics analysis revealed that ribosomal proteins are the main targets of K63 ubiquitination under stress. Moreover, we determine that accumulation of K63 ubiquitinated ribosomes relies on the activity of two redox-sensitive ubiquitin enzymes: the E2 conjugase Rad6 and the deubiquitinating enzyme Ubp2. Activity and cryo-EM structural analysis revealed that K63 ubiquitin modifies fully assembled monosomes and polysomes and is required for pausing translation at the elongation step. We named this pathway Redox control of Translation by Ubiquitin (RTU), a novel mechanism that supports cellular resistance to stress by aiding the reprogramming of gene expression at the translational level.