title: Persistence of an alternate chromatin structure at silenced loci in the absence of silencers.
abstract: In Saccharomyces cerevisiae, genes placed near telomeres or the silent HML and HMR mating-type loci are transcriptionally repressed by a heterochromatin-like structure. We have generated nonreplicating DNA rings by recombination in vivo to examine the role of chromosomal context on transcriptional repression. Specifically, recombination at HMR was used to produce rings that lacked the E and I silencers. An altered level of DNA supercoiling was observed in these rings but not in comparable rings from derepressed loci. Our results indicate that a repressive chromatin structure persists in an extrachromosomal environment immediately following removal of the cis-acting control elements. Examination of both chromatin footprints and DNA sequence dependence revealed that changes in nucleosome number could account for the topology shifts. Upon continued cell growth, the differences in supercoiling were lost and transcriptional competence was restored. These results show that silencers are required for sustained persistence of repressive chromatin structure, even in the absence of DNA replication.
authors.affiliation: Department of Pharmacology, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA.
authors.forename: T H
authors.initials: TH
authors.lastname: Cheng
authors.forename: Y C
authors.initials: YC
authors.lastname: Li
authors.forename: M R
authors.initials: MR
authors.lastname: Gartenberg
mesh_terms: D002843:Chromatin / Q000648:ultrastructure*; D018983:DNA Footprinting; D004271:DNA, Fungal / Q000737:chemistry; D004278:DNA, Superhelical / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000502:physiology*; D005656:Fungal Proteins / Q000502:physiology*; D015966:Gene Expression Regulation, Fungal; D005809:Genes, Regulator / Q000502:physiology*; D006655:Histone Deacetylases; D009690:Nucleic Acid Conformation; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D015534:Trans-Activators / Q000502:physiology*
chemical_list: D002843:Chromatin; D004271:DNA, Fungal; D004278:DNA, Superhelical; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C084121:SIR1 protein, S cerevisiae; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D015534:Trans-Activators; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases