title: Cti6, a PHD domain protein, bridges the Cyc8-Tup1 corepressor and the SAGA coactivator to overcome repression at GAL1.
abstract: The yeast Cyc8 and Tup1 proteins form a corepressor complex that, when tethered to DNA, turns off transcription. Release of the Cyc8-Tup1 corepressor from a promoter has been considered as a prerequisite for subsequent transcriptional activation. Contrasting this, we demonstrate that Cyc8-Tup1 is continuously associated with target promoters under both repressive and inducing conditions. At the GAL1 promoter, Cyc8-Tup1 facilitates recruitment of SAGA (Spt-Ada-Gcn5-acetyltranferase) via Cti6, a PHD domain protein that physically links the Cyc8-Tup1 and SAGA complexes. Lack of functional corepressor renders GAL1 transcription largely independent of specific SAGA subunits. Thus, corepressor's release is not the mechanism of derepression; instead, it is the coactivator complex that alleviates Cyc8-Tup1-mediated repression under induction conditions.
authors.affiliation: Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology, Biology Department, University of Crete, P.O. Box 1527, Vassilika Vouton, 711 10 Heraklion, Crete, Greece
authors.forename: Manolis
authors.initials: M
authors.lastname: Papamichos-Chronakis
authors.forename: Theodoros
authors.initials: T
authors.lastname: Petrakis
authors.forename: Eleni
authors.initials: E
authors.lastname: Ktistaki
authors.forename: Irini
authors.initials: I
authors.lastname: Topalidou
authors.forename: Dimitris
authors.initials: D
authors.lastname: Tzamarias
mesh_terms: D004268:DNA-Binding Proteins; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: C065455:CYC8 protein, S cerevisiae; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; C066502:TUP1 protein, S cerevisiae; D014157:Transcription Factors