title: Differential Phosphorylation of RNA Polymerase III and the Initiation Factor TFIIIB in Saccharomyces cerevisiae.
abstract: The production of ribosomes and tRNAs for protein synthesis has a high energetic cost and is under tight transcriptional control to ensure that the level of RNA synthesis is balanced with nutrient availability and the prevailing environmental conditions. In the RNA polymerase (pol) III system in yeast, nutrients and stress affect transcription through a bifurcated signaling pathway in which protein kinase A (PKA) and TORC1 activity directly or indirectly, through downstream kinases, alter the phosphorylation state and function of the Maf1 repressor and Rpc53, a TFIIF-like subunit of the polymerase. However, numerous lines of evidence suggest greater complexity in the regulatory network including the phosphoregulation of other pol III components. To address this issue, we systematically examined all 17 subunits of pol III along with the three subunits of the initiation factor TFIIIB for evidence of differential phosphorylation in response to inhibition of TORC1. A relatively high stoichiometry of phosphorylation was observed for several of these proteins and the Rpc82 subunit of the polymerase and the Bdp1 subunit of TFIIIB were found to be differentially phosphorylated. Bdp1 is phosphorylated on four major sites during exponential growth and the protein is variably dephosphorylated under conditions that inhibit tRNA gene transcription. PKA, the TORC1-regulated kinase Sch9 and protein kinase CK2 are all implicated in the phosphorylation of Bdp1. Alanine substitutions at the four phosphosites cause hyper-repression of transcription indicating that phosphorylation of Bdp1 opposes Maf1-mediated repression. The new findings suggest an integrated regulatory model for signaling events controlling pol III transcription.
authors.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America.
authors.forename: Jaehoon
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America.
authors.forename: Robyn D
authors.initials: RD
authors.lastname: Moir
authors.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America; Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America.
authors.forename: Ian M
authors.initials: IM
authors.lastname: Willis
mesh_terms: D017868:Cyclic AMP-Dependent Protein Kinases; D015966:Gene Expression Regulation, Fungal; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases; D012320:RNA Polymerase III / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D035361:Transcription Factor TFIIIB / Q000378:metabolism*; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: C474805:Bdp1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C561842:TORC1 protein complex, S cerevisiae; D035361:Transcription Factor TFIIIB; D014157:Transcription Factors; D017346:Protein Serine-Threonine Kinases; C530964:SCH9 protein, S cerevisiae; D017868:Cyclic AMP-Dependent Protein Kinases; D012320:RNA Polymerase III; D020123:Sirolimus