There are three polymerases that contribute to RNA synthesis in eukaryotic cell. RNA polymerase III (Pol III) generates tRNAs, that have a central role in biology as an adaptor between codon information in DNA in the nucleus and translation of this information into proteins in the cytoplasm. Transcribed in nucleus, tRNAs undergo processing and numerous modifications before reaching the final destination in cytoplasm where translation occurs. The sequential action of these processes is responsible for the high translation fidelity and regulates translation rate in response to environmental signals.

In yeast Saccharomyces cerevisiae, Maf1 is the only known global and general Pol III repressor which mediates numerous stress signals. Maf1 is under the control of the TOR signaling pathway as a substrate of PP2A phosphatase Transcription regulation by Maf1 is, however, not limited to stress but is important for physiological changes between fermentation and respiration. Maf1 phosphorylation and intracellular distribution differ in cells growing in media with glucose from those grown on a nonfermentable carbon source. Moreover, following shift from glucose to nonfermentable carbon source, Maf1 decreases the levels of different tRNAs to a various extent. This conclusion is confirmed by quantification of microarray and by quantitative PCR on selected tRNA gene families. The absence of control of tRNA synthesis, mediated by Maf1, impairs cell viability under the respiratory conditions. The respiratory phenotype of maf1-Δ allowed genetic suppression studies toward dissection of the mechanism of Maf1 action on the Pol III transcription apparatus.

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1. Maf1 is involved in coupling carbon metabolism to RNA Polymerase III transcription