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Molecular and Cellular Biology, June 2005, p. 4514-4528, Vol. 25, No. 11
0270-7306/05/$08.00+0 doi:10.1128/MCB.25.11.4514-4528.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
A Nonhistone Protein-Protein Interaction Required for Assembly of the SIR Complex and Silent Chromatin
Adam D. Rudner,1
Brian E. Hall,2
Tom Ellenberger,2 and
Danesh Moazed1*
Department of Cell Biology,1
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Ave., Boston, Massachusetts 021152
Received 25 August 2004/
Returned for modification 21 October 2004/
Accepted 22 February 2005
Budding yeast silent chromatin, or heterochromatin, is composed of histones and the Sir2, Sir3, and Sir4 proteins. Their assembly into silent chromatin is believed to require the deacetylation of histones by the NAD-dependent deacetylase Sir2 and the subsequent interaction of Sir3 and Sir4 with these hypoacetylated regions of chromatin. Here we explore the role of interactions among the Sir proteins in the assembly of the SIR complex and the formation of silent chromatin. We show that significant fractions of Sir2, Sir3, and Sir4 are associated together in a stable complex. When the assembly of Sir3 into this complex is disrupted by a specific mutation on the surface of the C-terminal coiled-coil domain of Sir4, Sir3 is no longer recruited to chromatin and silencing is disrupted. Because in sir4 mutant cells the association of Sir3 with chromatin is greatly reduced despite the partial Sir2-dependent deacetylation of histones near silencers, we conclude that histone deacetylation is not sufficient for the full recruitment of silencing proteins to chromatin and that Sir-Sir interactions are essential for the assembly of heterochromatin.
* Corresponding author. Mailing address: Harvard Medical School, Department of Cell Biology, 240 Longwood Ave., Boston, MA 02115. Phone: (617) 432-1258. Fax: (617) 432-1144. E-mail: danesh{at}hms.harvard.edu.
Supplemental material for this article may be found at http://mcb.asm.org/.
Molecular and Cellular Biology, June 2005, p. 4514-4528, Vol. 25, No. 11
0022-538X/05/$08.00+0 doi:10.1128/MCB.25.11.4514-4528.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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Copyright © 2005 by the American Society for Microbiology. All rights reserved.