SILENCING AND HERITABLE DOMAINS OF GENE-EXPRESSION

Silencing is a process that assembles particular regions of eukaryotic chromosomes into transcriptionally inactive chromatin structures. Sil encing 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 inclu de transcription factors and the origin recognition complex (ORC). Sil encing has three recognizably separate phases: establishment, maintena nce, and inheritance. At least some silencers are origins of replicati on, and the establishment of the silenced state requires an S phase-sp ecific event. Once established, the silenced state is heritable, even in the absence of proteins required for its establishment. The silenci ng of mating-type genes bears many similarities to telomere position e ffects, and the two processes require many of the same proteins.