1zbx
From Proteopedia
Crystal structure of a Orc1p-Sir1p complex
Structural highlights
Function[ORC1_YEAST] Component of the origin recognition complex (ORC) that binds origins of replication. It has a role in both chromosomal replication and mating type transcriptional silencing. Binds to the ARS consensus sequence (ACS) of origins of replication.[1] [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.[2] [3] [4] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe interaction between silence information regulator 1 protein (Sir1p) and origin recognition complex 1 protein (Orc1p), the largest subunit of the origin recognition complex, plays an important role in the establishment of transcriptional silencing at the cryptic mating-type gene loci in Saccharomyces cerevisiae. Sir1p binds the N-terminal region of Orc1p encompassing a Bromo-adjacent homology (BAH) domain found in various chromatin-associated proteins. To understand the molecular mechanism of Sir protein recruitment, we have determined a 2.5-A cocrystal structure of the N-terminal domain of Orc1p in complex with the Orc1p-interacting domain of Sir1p. The structure reveals that Sir1p Orc1p-interacting domain has a bilobal structure: an alpha/beta N-terminal lobe and a C-terminal lobe resembling the Tudor domain royal family fold. The N-terminal lobe of Sir1p binds in a shallow groove between a helical subdomain and the BAH domain of Orc1p. The structure provides a mechanistic understanding of Orc1p-Sir1p interaction specificity, as well as insights into protein-protein interactions involving BAH domains in general. Structural basis for origin recognition complex 1 protein-silence information regulator 1 protein interaction in epigenetic silencing.,Hsu HC, Stillman B, Xu RM Proc Natl Acad Sci U S A. 2005 Jun 14;102(24):8519-24. Epub 2005 Jun 3. PMID:15937111[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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