The Sir1 protein's association with a silenced chromososome domain

Sir1 protein, one of four Sir proteins needed for assembly of silenced chromatin domains in Saccharomyces cerevisiae, and its role in silencing HMR, a cryptic mating-type locus are discussed. Sir1p was in very low concentrations in yeast cells but associated with HMR at all cell cycle states seen. Mechanisms that set up and inhibit assembly of silenced chromatin to a few discrete chromosomal domains and the origin recognition complex have been investigated.