Sir-mediated repression can occur independently of chromosomal and subnuclear contexts.
Epigenetic mechanisms silence the HM mating-type loci in budding yeast. These loci are tightly linked to telomeres, which are also repressed and held together in clusters at the nuclear periphery, much like mammalian heterochromatin. Yeast telomere anchoring can occur in the absence of silent chromatin through the DNA end binding factor Ku. Here we examine whether silent chromatin binds the nuclear periphery independently of telomeres and whether silencing persists in the absence of anchorage. HMR was excised from the chromosome by inducible site-specific recombination and tracked by real-time fluorescence microscopy. Silent rings associate with the nuclear envelope, while nonsilent rings move freely throughout the nucleus. Silent chromatin anchorage requires the action of either Ku or Esc1. In the absence of both proteins, rings move throughout the nucleoplasm yet remain silent. Thus, transcriptional repression can be sustained without perinuclear anchoring.
Gartenberg
Marc R
MR
Department of Pharmacology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA. gartenbe@umdnj.edu
Neumann
Frank R
FR
Laroche
Thierry
T
Blaszczyk
Marek
M
Gasser
Susan M
SM
D034961:Antigens, Nuclear / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D015825:Chromosomes, Fungal / Q000235:genetics* / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D020868:Gene Silencing; D000072200:Ku Autoantigen; D009685:Nuclear Envelope / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000378:metabolism
D034961:Antigens, Nuclear; D002843:Chromatin; D004268:DNA-Binding Proteins; C495981:Esc1 protein, S cerevisiae; D009687:Nuclear Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D000072200:Ku Autoantigen