Up-regulation of tRNA biosynthesis affects translational readthrough in maf1-Δ mutant of Saccharomyces cerevisiae

Maf1p is a negative effector of RNA polymerase III in yeast. The maf1-Δ mutation caused an increase in the level of cellular tRNAs, but a decrease of translational readthrough at nonsense codons. Using the lacZ-luc dual gene reporter system, we detected an almost twofold diminution of UAA and UAG readthrough in maf1-Δ compared with the parental strain. The maf1-Δ mutation did not affect the rate of protein biosynthesis and growth at standard conditions, but resulted in temperature-sensitive growth on non-fermentable carbon sources. We examined the correlation of the temperature sensitive and antisuppression phenotypes of maf1-Δ using a colour phenotype assay in the ade2-1 SUP11 strain. Antisuppression, but not the temperature-sensitive growth defect, was compensated either by increased dosage of SUP11 or by [PSI+], the prion form of the translation termination factor Sup35p. Summarizing, the elevated tRNA levels in maf1-Δ increase translational fidelity and, independently, affect growth under special conditions.