Open AccessA Silencer Promotes the Assembly of Silenced Chromatin Independently of Recruitment
Author(s) -
Patrick J. Lynch,
Laura N. Rusché
Publication year - 2009
Publication title -
molecular and cellular biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.14
H-Index - 327
eISSN - 1067-8824
pISSN - 0270-7306
DOI - 10.1128/mcb.00983-08
Subject(s) - biology , chromatin , telomere , genetics , chromatin immunoprecipitation , silencer , saccharomyces cerevisiae , gene silencing , computational biology , gene , promoter , gene expression , mechanical engineering , engineering , inlet
InSaccharomyces cerevisiae , silenced chromatin occurs at telomeres and the silent mating-type lociHMR andHML . At these sites, the Sir proteins are recruited to a silencer and then associate with adjacent chromatin. We used chromatin immunoprecipitation to compare the rates of Sir protein assembly at different genomic locations and discovered that establishment of silenced chromatin was much more rapid atHMR than at the telomere VI-R. Silenced chromatin also assembled more quickly on one side ofHMR-E than on the other. Despite differences in spreading, the Sir proteins were recruited toHMR-E and telomeric silencers at equivalent rates. Additionally, insertion ofHMR-E adjacent to the telomere VI-R increased the rate of Sir2p association with the telomere. These data suggest thatHMR-E functions to both recruit Sir proteins and promote their assembly across several kilobases. Observations that association of Sir2p occurs simultaneously throughoutHMR and that silencing atHMR is insensitive to coexpression of catalytically inactive Sir2p suggest thatHMR-E acts by enabling assembly to occur in a nonlinear fashion. The ability of silencers to promote assembly of silenced chromatin over several kilobases is likely an important mechanism for maintaining what would otherwise be unstable chromatin at the correct genomic locations.