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Structural basis for origin recognition complex 1 protein-silence information regulator 1 protein interaction in epigenetic silencing.

The 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.

Pubmed ID: 15937111


  • Hsu HC
  • Stillman B
  • Xu RM


Proceedings of the National Academy of Sciences of the United States of America

Publication Data

June 14, 2005

Associated Grants

  • Agency: NCI NIH HHS, Id: CA13106
  • Agency: NIGMS NIH HHS, Id: GM 63716
  • Agency: NIGMS NIH HHS, Id: GM45436
  • Agency: NIGMS NIH HHS, Id: R01 GM045436

Mesh Terms

  • Amino Acid Sequence
  • Crystallography
  • DNA-Binding Proteins
  • Epigenesis, Genetic
  • Escherichia coli
  • Gene Silencing
  • Models, Molecular
  • Molecular Sequence Data
  • Origin Recognition Complex
  • Protein Binding
  • Protein Structure, Tertiary
  • Saccharomyces cerevisiae
  • Silent Information Regulator Proteins, Saccharomyces cerevisiae