1z1a
From Proteopedia
S. cerevisiae Sir1 ORC-interaction domain
Structural highlights
Function[SIR1_YEAST] Involved in the establishment, but not the maintenance, of heterochromatic silencing at the cryptic mating-type loci HMR and HML. Is recruited by interacting with the ORC1 subunit of the origin recognition complex (ORC), which binds to HML-I or HMR-E silencers, DNA elements that direct the formation of silent chromatin at the mating-type loci. Establishes transcriptional silencing by recruiting the three other SIR proteins, SIR2, SIR3, and SIR4, that function directly in silenced chromatin and establish repression. Also found in centromeric chromatin. Binds to and helps retain CAC1, a subunit of chromatin assembly factor I (CAF-I) at centromeric loci independent on the other SIR proteins.[1] [2] [3] Publication Abstract from PubMedThe Sir1 protein plays a key role in establishing a silent chromatin structure at the cryptic mating-type loci HMR and HML in Saccharomyces cerevisiae by interacting with the bromo-adjacent homology (BAH) domain of the Orc1p subunit of the origin recognition complex (ORC). Here, we present the high-resolution crystal structures of the ORC interaction region (OIR) of Sir1p and that of the complex formed between the OIR and BAH domains. Amino acids within the OIR previously shown to be required for a Sir1p/ORC interaction are presented on a conserved, convex surface that forms a complementary interface with a concave region of the Orc1 BAH domain that is critical for transcriptional silencing. The OIR/BAH interaction surface comprises a network of hydrophobic and polar/ionic interactions between discrete structural modules in each protein and involves several residues that were not implicated in previous studies. These data provide important structural insights into a protein-protein interaction critical for the formation of a specialized chromatin domain within eukaryotic chromosomes. Structural basis of the Sir1-origin recognition complex interaction in transcriptional silencing.,Hou Z, Bernstein DA, Fox CA, Keck JL Proc Natl Acad Sci U S A. 2005 Jun 14;102(24):8489-94. Epub 2005 Jun 2. PMID:15932939[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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