Regulation of RNA polymerase III transcription by Maf1 protein.
Maf1 was the first protein discovered to regulate polymerase III RNA in yeast and because it is evolutionarily conserved, a Maf1 ortholog also serves to restrain transcription in mouse and human cells. Understanding the mechanism of the regulation has been made possible by recent studies showing that Maf1 is a nuclear/cytoplasmic protein whose subcellular distribution and hence negative regulation of Pol III transcription is mediated by the nutrient-sensing signaling pathways, TOR and RAS. Under stress conditions and during growth in a nonfermentable carbon source Maf1 is dephosphorylated and imported to the nucleus. In its non-phosphorylated form, Maf1 interacts with the polymerase III transcription machinery. Phosphorylation serves to locate Maf1 to the cytoplasm under favorable growth conditions, thereby preventing it from non-negatively regulating polymerase III when high levels of tRNA transcription are required. Relocation of Maf1 to the cytoplasm is dependent on Msn5, a carrier responsible for export of several other phosphoproteins out of the nucleus. The absence of Maf1-mediated control of tRNA synthesis impairs yeast viability in nonfermentable carbon sources. Moreover, in cells grown in a nonfermentable carbon source, Maf1 regulates the levels of different tRNAs to various extents. This differential regulation may contribute to the physiological role of Maf1.
Cieśla
Małgorzata
M
Department of Genetics, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warszawa, Poland.
Boguta
Magdalena
M
D000595:Amino Acid Sequence; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D010766:Phosphorylation; D012320:RNA Polymerase III / Q000235:genetics* / Q000378:metabolism*; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
C104954:MAF1 protein, S cerevisiae; D012331:RNA, Fungal; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D012343:RNA, Transfer; D012320:RNA Polymerase III