Overexpression of genes encoding tRNATyr and tRNAGln increases the viability of Saccharomyces cerevisiae strains with nonsense mutations in the SUP45 gene

At present, the machinery supporting the viability of organisms possessing nonsense mutations in essential genes is not entirely understood. Nonsense mutants of Saccharomyces cerevisiae yeast containing a premature translation termination codon in the essential SUP45 gene are known. These strains are viable in the absence of mutant suppressor tRNAs; hence, the existence of alternative mechanisms providing nonsense suppression and mutant viability is conjectured. Analysis of clones obtained by transformation of a strain bearing a nonsense-mutant allele of SUP45 with a multicopy yeast genomic library revealed three genes encoding wild-type tRNATyr and four genes encoding wild-type tRNAGln, which increased nonsense mutant viability. Moreover, overexpression of these genes leads to an increase in the amount of the full-length eRF1 protein in cells and compensates for heat sensitivity in the nonsense mutants. Probable ways of tRNATyr and tRNAGln influence on the increase in the viability of strains with nonsense mutations in SUP45 are discussed.