title: TOR-dependent reduction in the expression level of Rrn3p lowers the activity of the yeast RNA Pol I machinery, but does not account for the strong inhibition of rRNA production.
abstract: Ribosome biogenesis is tightly linked to cellular growth. A crucial step in the regulation of ribosomal RNA (rRNA) gene transcription is the formation of the complex between RNA polymerase I (Pol I) and the Pol I-dependent transcription factor Rrn3p. We found that TOR inactivation leads to proteasome-dependent degradation of Rrn3p and a strong reduction in initiation competent Pol I-Rrn3p complexes affecting yeast rRNA gene transcription. Using a mutant expressing non-degradable Rrn3p or a strain in which defined endogenous Rrn3p levels can be adjusted by the Tet-off system, we can demonstrate that Rrn3p levels influence the number of Pol I-Rrn3p complexes and consequently rRNA gene transcription. However, our analysis reveals that the dramatic reduction of rRNA synthesis in the immediate cellular response to impaired TOR signalling cannot be explained by the simple down-regulation of Rrn3p and Pol I-Rrn3p levels.
authors.affiliation: Institut für Biochemie, Genetik und Mikrobiologie, Universität Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany.
authors.forename: Anja
authors.initials: A
authors.lastname: Philippi
authors.forename: Robert
authors.initials: R
authors.lastname: Steinbauer
authors.forename: Alarich
authors.initials: A
authors.lastname: Reiter
authors.forename: Stephan
authors.initials: S
authors.lastname: Fath
authors.forename: Isabelle
authors.initials: I
authors.lastname: Leger-Silvestre
authors.forename: Philipp
authors.initials: P
authors.lastname: Milkereit
authors.forename: Joachim
authors.initials: J
authors.lastname: Griesenbeck
authors.forename: Herbert
authors.initials: H
authors.lastname: Tschochner
mesh_terms: D020459:Genes, rRNA; D035463:Pol1 Transcription Initiation Complex Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012318:RNA Polymerase I / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000096:biosynthesis* / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000032:analysis / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D020123:Sirolimus / Q000494:pharmacology; D014158:Transcription, Genetic; D054875:Ubiquitination
chemical_list: D035463:Pol1 Transcription Initiation Complex Proteins; D012335:RNA, Ribosomal; C101161:RRN3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D017346:Protein Serine-Threonine Kinases; C500749:target of rapamycin protein, S cerevisiae; D012318:RNA Polymerase I; D046988:Proteasome Endopeptidase Complex; D020123:Sirolimus