Silencing and heritable domains of gene expression.

Silencing is a process that assembles particular regions of eukaryotic chromosomes into transcriptionally inactive chromatin structures. Silencing involves specialized regulatory sites known as silencers and a combination of general DNA-binding proteins and proteins dedicated to silencing. In the yeast Saccharomyces cerevisiae, these proteins include transcription factors and the origin recognition complex (ORC). Silencing has three recognizably separate phases: establishment, maintenance, and inheritance. At least some silencers are origins of replication, and the establishment of the silenced state requires an S phase-specific event. Once established, the silenced state is heritable, even in the absence of proteins required for its establishment. The silencing of mating-type genes bears many similarities to telomere position effects, and the two processes require many of the same proteins.