Genetic background and mistranslation frequency determine the impact of mistranslating tRNASerUGG

Transfer RNA variants increase the frequency of mistranslation, the mis-incorporation of an amino acid not specified by the "standard" genetic code, to frequencies approaching 10% in yeast and bacteria. Cells cope with these variants by having multiple copies of each tRNA isodecoder and through pathways that deal with proteotoxic stress. In this study, we define the genetic interactions of the gene encoding tRNASerUGG,G26A, which mistranslates serine at proline codons. Using a collection of yeast temperature sensitive alleles, we identify negative synthetic genetic interactions between the mistranslating tRNA and 109 alleles representing 91 genes, with nearly half of the genes having roles in RNA processing or protein folding and turnover. By regulating tRNA expression, we then compare the strength of the negative genetic interaction for a subset of identified alleles under differing amounts of mistranslation. The frequency of mistranslation correlated with impact on cell growth for all strains analyzed; however, there were notable differences in the extent of the synthetic interaction at different frequencies of mistranslation depending on the genetic background. For many of the strains the extent of the negative interaction with tRNASerUGG,G26A was proportional to the frequency of mistranslation or only observed at intermediate or high frequencies. For others the synthetic interaction was approximately equivalent at all frequencies of mistranslation. As humans contain similar mistranslating tRNAs these results are important when analyzing the impact of tRNA variants on disease, where both the individuals genetic background and the expression of the mistranslating tRNA variant need to be considered.