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.
Department of Genetics, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warszawa, Poland.
Małgorzata
M
Cieśla
Magdalena
M
Boguta
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