Toward Biochemical Understanding of a Transcriptionally Silenced Chromosomal Domain in Saccharomyces cerevisiae

A few discrete portions of the Saccharomyces cerevisiae genome, such as the chromosome ends within 5–10 kilobase pairs (kb) of telomeres and the silent mating-type regions named HMR and HML, are defined as transcriptionally silent because they cause repression of an RNA polymerase II gene placed within them (reviewed comprehensively in Ref. 1). S. cerevisiae silencing is a form of transcriptional repression that is long range, occurring over distances larger than a single gene. Silencing occurs in only certain chromosomal regions and depends more on a gene's position in the genome than its promoter sequence.