The Swi/Snf chromatin remodeling complex is required for ribosomal dna and telomeric silencing in Saccharomyces cerevisiae

The Swi/Snf chromatin remodeling complex has been previously demonstrated to be required for transcrip-tional activation and repression of a subset of genes in Saccharomyces cerevisiae. In this work we demonstrate that Swi/Snf is also required for repression of RNA polymerase II-dependent transcription in the ribosomal DNA (rDNA) locus (rDNA silencing). This repression appears to be independent of both Sir2 and Set1, two factors known to be required for rDNA silencing. In contrast to many other rDNA silencing mutants that have elevated levels of rDNA recombination, snf2 mutants have a significantly decreased level of rDNA recombi-nation. Additional studies have demonstrated that Swi/Snf is also required for silencing of genes near telomeres while having no detectable effect on silencing of HML or HMR. The Saccharomyces cerevisiae Swi/Snf complex is an ATP-dependent chromatin remodeling complex that can activate or repress transcription (see references 3, 34, and 44 for recent reviews). Swi/Snf contains 11 different subunits, including Snf2, a highly conserved ATPase. The Snf2 subunit is the catalytic core of Swi/Snf; single amino acid changes in the DNA-depen-dent ATPase domain eliminate both the ATPase activity an