Expanded roles of the origin recognition complex in the architecture and function of silenced chromatin in Saccharomyces cerevisiae.
The silenced chromatin at the cryptic mating-type loci (HML and HMR) of Saccharomyces cerevisiae requires a cell cycle event between early S phase and G(2)/M phase to achieve repression. Although DNA replication per se is not essential for silencing, mutations in many of the proteins involved in DNA replication affect silencing. Each of the four silencers, which flank the silenced loci, includes an origin recognition complex (ORC) binding site (ACS). ORC directly interacted with Sir1 and recruits Sir1 to the silencers. This study describes additional roles for ORC in the architecture of silenced chromatin. Using chromatin immunoprecipitation (ChIP) analysis, we found that ORC physically interacts throughout the internal regions of HMR as well as with silencers. This interaction depended on the presence of Sir proteins and, in part, on the HMR-I silencer. ORC remained associated with the internal regions of HMR even when these regions were recombinationally separated from the silencers. Moreover, ORC could be recruited to the silencers lacking an ACS through its Sir1 interaction.
Ozaydin
Bilge
B
Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3220, USA.
Rine
Jasper
J
D002843:Chromatin / Q000378:metabolism*; D004261:DNA Replication / Q000235:genetics; D015966:Gene Expression Regulation, Fungal; D020868:Gene Silencing; D049770:Genes, Mating Type, Fungal; D051738:Origin Recognition Complex / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000378:metabolism
D002843:Chromatin; D051738:Origin Recognition Complex; C084121:SIR1 protein, S cerevisiae; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae