An ARS element inhibits DNA replication through a SIR2-Dependent mechanism

During G1 phase, a prereplicative complex (pre-RC) that determines where DNA synthesis initiates forms at origins. The Sir2p histone deacetylase inhibits pre-RC assembly at a subset of origins, suggesting that Sir2p, inhibits DNA replication through a unique aspect of origin structure. Here, we identified five SIR2-sensitive origins on chromosomes III and VI . Linker scan analysis of two origins indicated that they share a common organization, including an inhibitory sequence positioned 3' to the sites of origin recognition complex (ORC) binding and pre-RC assembly. This inhibitory sequence (I-s) required SIR2 for its activity, suggesting that SIR2 inhibits origins through this sequence. Furthermore, Is elements occurred within positioned nucleosomes, and Abf1 p-mediated exclusion of nucleosomes from the origin abrogated the inhibition. These data suggest that Sir2p, and Is elements inhibit origin activity by promoting an unfavorable chromatin structure for pre-RC assembly.