title: The conserved core of a human SIR2 homologue functions in yeast silencing.
abstract: Silencing is a universal form of transcriptional regulation in which regions of the genome are reversibly inactivated by changes in chromatin structure. Sir2 (Silent Information Regulator) protein is unique among the silencing factors in Saccharomyces cerevisiae because it silences the rDNA as well as the silent mating-type loci and telomeres. Discovery of a gene family of Homologues of Sir Two (HSTs) in organisms from bacteria to humans suggests that SIR2's silencing mechanism might be conserved. The Sir2 and Hst proteins share a core domain, which includes two diagnostic sequence motifs of unknown function as well as four cysteines of a putative zinc finger. We demonstrate by mutational analyses that the conserved core and each of its motifs are essential for Sir2p silencing. Chimeras between Sir2p and a human Sir2 homologue (hSir2Ap) indicate that this human protein's core can substitute for that of Sir2p, implicating the core as a silencing domain. Immunofluorescence studies reveal partially disrupted localization, accounting for the yeast-human chimeras' ability to function at only a subset of Sir2p's target loci. Together, these results support a model for the involvement of distinct Sir2p-containing complexes in HM/telomeric and rDNA silencing and that HST family members, including the widely expressed hSir2A, may perform evolutionarily conserved functions.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, Porter Biosciences, University of Colorado, Boulder, Colorado 80309-0347, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Sherman
authors.forename: E M
authors.initials: EM
authors.lastname: Stone
authors.forename: L L
authors.initials: LL
authors.lastname: Freeman-Cook
authors.forename: C B
authors.initials: CB
authors.lastname: Brachmann
authors.forename: J D
authors.initials: JD
authors.lastname: Boeke
authors.forename: L
authors.initials: L
authors.lastname: Pillus
mesh_terms: D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000378:metabolism; D015825:Chromosomes, Fungal / Q000235:genetics; D017124:Conserved Sequence / Q000235:genetics / Q000502:physiology*; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D004275:DNA, Ribosomal / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D005786:Gene Expression Regulation; D005799:Genes, Dominant / Q000235:genetics / Q000502:physiology; D005800:Genes, Fungal / Q000235:genetics; D049770:Genes, Mating Type, Fungal; D005816:Genetic Complementation Test; D006655:Histone Deacetylases; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D056564:Sirtuin 1; D056565:Sirtuin 2; D037761:Sirtuins; D013329:Structure-Activity Relationship; D016615:Telomere / Q000235:genetics; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D015534:Trans-Activators; C087778:SIR2 protein, S cerevisiae; C447939:SIRT1 protein, human; D056564:Sirtuin 1; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases; D003545:Cysteine