title: Role of the conserved Sir3-BAH domain in nucleosome binding and silent chromatin assembly.
abstract: Silent chromatin domains in Saccharomyces cerevisiae represent examples of epigenetically heritable chromatin. The formation of these domains involves the recruitment of the SIR complex, composed of Sir2, Sir3, and Sir4, followed by iterative cycles of NAD-dependent histone deacetylation and spreading of SIR complexes over adjacent chromatin domains. We show here that the conserved bromo-adjacent homology (BAH) domain of Sir3 is a nucleosome- and histone-tail-binding domain and that its binding to nucleosomes is regulated by residues in the N terminus of histone H4 and the globular domain of histone H3 on the exposed surface of the nucleosome. Furthermore, using a partially purified system containing nucleosomes, the three Sir proteins, and NAD, we observe the formation of SIR-nucleosome filaments with a diameter of less than 20 nm. Together, these observations suggest that the SIR complex associates with an extended chromatin fiber through interactions with two different regions in the nucleosome.
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Megumi
authors.initials: M
authors.lastname: Onishi
authors.forename: Gunn-Guang
authors.initials: GG
authors.lastname: Liou
authors.forename: Johannes R
authors.initials: JR
authors.lastname: Buchberger
authors.forename: Thomas
authors.initials: T
authors.lastname: Walz
authors.forename: Danesh
authors.initials: D
authors.lastname: Moazed
mesh_terms: D000123:Acetyltransferases / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics / Q000502:physiology; D042002:Chromatin Assembly and Disassembly; D047369:Chromatin Immunoprecipitation; D020868:Gene Silencing; D006657:Histones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008854:Microscopy, Electron; D008958:Models, Molecular; D009154:Mutation; D009707:Nucleosomes / Q000378:metabolism* / Q000648:ultrastructure; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020349:Surface Plasmon Resonance
chemical_list: D006657:Histones; D009707:Nucleosomes; C084122:SIR3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D000123:Acetyltransferases