RNA polymerase III (Pol III) produces essential components of the biosynthetic machinery and therefore its activity is tightly coupled with the cell growth and metabolism. In yeast Saccharomyces cerevisiae, Maf1 is the only known global and direct Pol III repressor which mediates numerous stress signals. Here we demonstrate that transcription regulation by Maf1 is not limited to stress but is important for physiological changes between fermentation and respiration. Under respiratory conditions Maf1 is activated by dephosphorylation and import to the nucleus. Transition from a nonfermentable carbon source to glucose induces Maf1 phosphorylation and its relocation to the cytoplasm. The absence of control of tRNA synthesis, mediated by Maf1, impairs cell viability on nonfermentable carbon sources. The respiratory phenotype of maf1-Δ allowed genetic suppression studies toward dissection of the mechanism of Maf1 action on the Pol III transcription apparatus. Moreover, in cells grown on a nonfermentable carbon source, Maf1 decreases the levels of different tRNAs to a various extent. The observation that not all tRNAs are equally regulated is new and may contribute to the physiological role of Maf1.

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1. Specific regulation of tRNA transcription