A role for a replicator dominance mechanism in silencing.
The role of the natural HMR-E silencer in modulating replication initiation and silencing by the origin recognition complex (ORC) was examined. When natural HMR-E was the only silencer controlling HMR, the silencer's ORC-binding site (ACS) was dispensable for replication initiation but essential for silencing, indicating that a non-silencer chromosomal replicator(s) existed in close proximity to the silencer. Further analysis revealed that regions flanking both sides of HMR-E contained replicators. In contrast to replication initiation by the intact silencer, initiation by the non-silencer replicator(s) was abolished in an orc2-1 mutant, indicating that these replicators were extremely sensitive to defects in ORC. Remarkably, the activity of one of the non-silencer replicators correlated with reduced silencing; inactivation of these replicators caused by either the orc2-1 mutation or the deletion of flanking sequences enhanced silencing. These data were consistent with a role for the ORC bound to the HMR-E silencer ACS in suppressing the function of neighboring ORC molecules capable of inhibiting silencing, and indicated that differences in ORC-binding sites within HMR itself had profound effects on ORC function. Moreover, replication initiation by natural HMR-E was inefficient, suggesting that closely spaced replicators within HMR contributed to an inhibition of replication initiation.
Palacios DeBeer
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MA
Department of Biomolecular Chemistry, 587 MSC 1300 University Avenue, University of Wisconsin, Madison, WI 53706-1532, USA.
Fox
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CA
D000483:Alleles; D001665:Binding Sites; D002455:Cell Division; D004261:DNA Replication / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D005800:Genes, Fungal / Q000235:genetics; D006655:Histone Deacetylases; D008957:Models, Genetic; D009154:Mutation; D051738:Origin Recognition Complex; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D018741:Replication Origin / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics* / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D016615:Telomere / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology; D014158:Transcription, Genetic / Q000235:genetics
D004268:DNA-Binding Proteins; C497215:ORC2 protein, S cerevisiae; D051738:Origin Recognition Complex; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D015534:Trans-Activators; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases