title: Structure of the coiled-coil dimerization motif of Sir4 and its interaction with Sir3.
abstract: The yeast silent information regulators Sir2, Sir3, and Sir4 physically interact with one another to establish a transcriptionally silent state by forming repressive chromatin structures. The Sir4 protein contains binding sites for both Sir2 and Sir3, and these protein-protein interactions are required for gene silencing. Here, we report the X-ray structure of the coiled-coil dimerization motif within the C-terminus of Sir4 and show that it forms a stable 1:1 complex with a dimeric fragment of Sir3 (residues 464-978). We have identified a cluster of residues on the surface of the Sir4 coiled coil required for specific interactions with Sir3. The histone deacetylase Sir2 can also bind to this complex, forming a ternary complex with the truncated Sir3 and Sir4 proteins. The dual interactions of Sir4 with Sir3 and Sir2 suggest a physical basis for recruiting Sir3 to chromatin by virtue of its interactions with Sir4 and with deacetylated histones in chromatin.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
authors.forename: Ju-Fang
authors.initials: JF
authors.lastname: Chang
authors.forename: Brian E
authors.initials: BE
authors.lastname: Hall
authors.forename: Jason C
authors.initials: JC
authors.lastname: Tanny
authors.forename: Danesh
authors.initials: D
authors.lastname: Moazed
authors.forename: David
authors.initials: D
authors.lastname: Filman
authors.forename: Tom
authors.initials: T
authors.lastname: Ellenberger
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D019281:Dimerization; D015966:Gene Expression Regulation, Fungal; D006655:Histone Deacetylases / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011487:Protein Conformation; D011489:Protein Denaturation; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D056565:Sirtuin 2; D037761:Sirtuins / Q000378:metabolism
chemical_list: C084122:SIR3 protein, S cerevisiae; C061573:SIR4 protein, S cerevisiae; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases