The Origin Recognition Complex, SIR1, and the S Phase Requirement for Silencing

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Science  06 Jun 1997:
Vol. 276, Issue 5318, pp. 1547-1551
DOI: 10.1126/science.276.5318.1547

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Silencing of transcription in Saccharomyces cerevisiaehas several links to DNA replication, including a role for the origin recognition complex (ORC), the DNA replication initiator, in both processes. In addition, the establishment of silencing at theHML and HMR loci requires cells to pass through the S phase of the cell cycle. Passage through S phase was required for silencing of HMR even under conditions in which ORC itself was no longer required. The requirement for ORC in silencing ofHMR could be bypassed by tethering the Sir1 protein to theHMR-E silencer. However, ORC had a Sir1-independent role in transcriptional silencing at telomeres. Thus, the role of ORC in silencing was separable from its role in initiation, and the role of S phase in silencing was independent of replication initiation at the silencers.

  • * Present address: Department of Biomolecular Chemistry, University of Wisconsin, 1300 University Avenue, Madison, WI 53706, USA.

  • To whom correspondence should be addressed. E-mail: jasper{at}

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