The proteins SIR1 through SIR4 are required for transcriptional repression of the silent mating type loci, HML and HMR (PubMed:18039933). The proteins SIR2 through SIR4 repress mulitple loci by modulating chromatin structure (PubMed:18039933). Involves the compaction of chromatin fiber into a more condensed form (PubMed:18039933). Homodimer (PubMed:12791253). Interacts with MPS3 (PubMed:18039933). Interacts with RIS1 (PubMed:9271422). Interacts with SIR1, SIR2 and SIR3 (PubMed:11722841). Interacts with YKU80 (PubMed:14551211). Interacts with UBP10 (PubMed:10490600, PubMed:26149687).