title: Cooperation at a distance between silencers and proto-silencers at the yeast HML locus.
abstract: Transcriptional repression at the silent yeast mating type loci is achieved through the formation of a particular nucleoprotein complex at specific cis-acting elements called silencers. This complex in turn appears to initiate the spreading of a histone binding protein complex into the surrounding chromatin, which restricts accessibility of the region to the transcription machinery. We have investigated long-range, cooperative effects between silencers by studying the repression of a reporter gene integrated at the HML locus flanked by various combinations of wild-type and mutated silencer sequences. Two silencers can cooperate over >4000 bp to repress transcription efficiently. More importantly, a single binding site for either the repressor activator protein 1 (Rap1), the autonomous replicating sequence (ARS) binding factor 1 (Abf1) or the origin recognition complex (ORC) can enhance the action of a distant silencer without acting as a silencer on its own. Functional cooperativity is demonstrated using a quantitative assay for repression, and varies with the affinity of the binding sites used. Since the repression mechanism is Sir dependent, the Rap1, ORC and/or Abf1 proteins bound to distant DNA elements may interact to create an interface of sufficiently high affinity such that Sir-containing complexes bind, nucleating the silent chromatin state.
authors.affiliation: Ecole Normale Supérieure de Lyon, France.
authors.forename: C
authors.initials: C
authors.lastname: Boscheron
authors.forename: L
authors.initials: L
authors.lastname: Maillet
authors.forename: S
authors.initials: S
authors.lastname: Marcand
authors.forename: M
authors.initials: M
authors.lastname: Tsai-Pflugfelder
authors.forename: S M
authors.initials: SM
authors.lastname: Gasser
authors.forename: E
authors.initials: E
authors.lastname: Gilson
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D006655:Histone Deacetylases; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000235:genetics; D020668:rap GTP-Binding Proteins
chemical_list: D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D009838:Oligodeoxyribonucleotides; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D015534:Trans-Activators; D001616:beta-Galactosidase; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases; D019204:GTP-Binding Proteins; D020668:rap GTP-Binding Proteins