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.
Department of Biomolecular Chemistry, 587 MSC 1300 University Avenue, University of Wisconsin, Madison, WI 53706-1532, USA.
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Palacios DeBeer
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Fox
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