Codon-specific effects of tRNA anticodon loop modifications on translational misreading errors in the yeast Saccharomyces cerevisiae

Protein synthesis requires both high speed and accuracy to ensure a healthy cellular environment. Estimates of errors during protein synthesis in Saccharomyces cerevisiae have varied from 10(−3) to 10(−4) errors per codon. Here, we show that errors made by [Formula: see text] in yeast can vary 100-fold, from 10(−6) to 10(−4) errors per codon. The most frequent errors require a G•U mismatch at the second position for the near cognate codon GGA (Gly). We also show, contrary to our previous results, that yeast tRNAs can make errors involving mismatches at the wobble position but with low efficiency. We have also assessed the effect on misreading frequency of post-transcriptional modifications of tRNAs, which are known to regulate cognate codon decoding in yeast. We tested the roles of mcm(5)s(2)U(34) and t(6)A(37) and show that their effects depend on details of the codon anticodon interaction including the position of the modification with respect to the base mismatch and the nature of that mismatch. Both mcm(5) and s(2) modification of wobble uridine strongly stabilizes G(2)•U(35) mismatches when [Formula: see text] misreads the GGA Gly codon but has weaker effects on other mismatches. By contrast, t(6)A(37) destabilizes U(1)•U(36) mismatches when [Formula: see text] misreads UAA or UAG but stabilizes mismatches at the second and wobble positions.