Regulation of translation after exposure to stress

Abstract

When encountering environmental stress, cells alter their gene expression pattern which primarily occurs at translational level. This leads to rapid changes in the protein repertoire, making the cells more able to adapt and survive the environmental stress. One such rapid change when cells are exposed to stress is a dramatic global downregulation of translation. It was for a long time a generally accepted view that this was a result of phosphorylation of the α subunit of the translation initiation factor eIF2, which was found to be upregulated after exposure to stress. Phosphorylation of eIF2α is performed by the eFI2α kinase Gcn2, which is activated by several stressors, including UV irradiation. Our group has previously demonstrated that the global depression of translation after UV irradiation is not dependent of Gcn2 or phosphorylation of eIF2α, as translation was still downregulated in S. pombe strains where Gcn2 and eFI2α phosphorylation were absent. This suggests that there is an alternative pathway responsible for global downregulation of translation after exposure to stress. To identify proteins that might be key players in regulating translation after UV exposure, our group used mass spectrometry. Several protein candidates were obtained that are involved in the novel regulatory mechanism. This study addresses three aspects of translational regulation after UV irradiation. First, we wish to verify the results of the mass spectrometry and in this work, I set out to construct the necessary strains. Second, we investigated the role of eIF2α phosphorylation further by measuring translation rates and viability in a non-phosphorylatable eIF2α mutant. Third, we investigated whether DNA damage is the signal for global regulation of translation by measuring translation rates in a DNA repair-mutant. We found that global downregulation of translation and recovery of translation after exposure to UV are not dependent on eIF2α phosphorylation. We also observed no change in viability after UV exposure when phosphorylation of eIF2α is absent. Finally, our findings strongly suggest that DNA damage is the signal for global downregulation of translation after exposure to UV.