Diverse and dynamic functions of the Sir silencing complex.

The yeast Sir protein complex has been implicated in transcriptional silencing and suppression of recombination. The Sir complex creates structured chromosomal domains at telomeres, silent mating-type loci and ribosomal DNA to invoke these functional states. Mechanistic insights into the function of Sir proteins implicate a range of activities in yeast, including repair of DNA double-strand breaks, regulation of the mitotic cell cycle, meiosis and ageing. I speculate that the Sir proteins may be capable of enzymatic modification of chromatin and other substrates, which enables them to carry out a broad range of cellular functions.