Elp3 and Dph3 of Schizosaccharomyces pombe mediate cellular stress responses through tRNALys UUU modifications

Efficient protein synthesis in eukaryotes requires diphthamide modification of translation elongation factor eEF2 and wobble uridine modifications of tRNAs. In higher eukaryotes, these processes are important for preventing neurological and developmental defects and cancer. In this study, we used Schizosaccharomyces pombe as a model to analyse mutants defective in eEF2 modification (dph1?), in tRNA modifications (elp3?), or both (dph3?) for sensitivity to cytotoxic agents and thermal stress. The dph3? and elp3? mutants were sensitive to a range of drugs and had growth defects at low temperature. dph3? was epistatic with dph1? for sensitivity to hydroxyurea and methyl methanesulfonate, and with elp3? for methyl methanesulfonate and growth at 16 °C. The dph1? and dph3? deletions rescued growth defects of elp3? in response to thiabendazole and at 37 °C. Elevated tRNALys UUU levels suppressed the elp3? phenotypes and some of the dph3? phenotypes, indicating that lack of tRNALys UUU modifications were responsible. Furthermore, we found positive genetic interactions of elp3? and dph3? with sty1? and atf1?, indicating that Elp3/Dph3-dependent tRNA modifications are important for efficient biosynthesis of key factors required for accurate responses to cytotoxic stress conditions.