Affiliation:
1. Department of Biochemistry and Molecular Biology, The Center for Gene Regulation, The Pennsylvania State University, University Park, Pennsylvania 16802
Abstract
ABSTRACT
Genetic studies have suggested that chromatin structure is involved in repression of the silent mating type loci in
Saccharomyces cerevisiae
. Chromatin mapping at nucleotide resolution of the transcriptionally silent
HML
α and the active
MAT
α shows that unique organized chromatin structure characterizes the silent state of
HML
α. Precisely positioned nucleosomes abutting the silencers extend over the α1 and α2 coding regions. The HO endonuclease recognition site, nuclease hypersensitive at
MAT
α, is protected at
HML
α. Although two precisely positioned nucleosomes incorporate transcription start sites at
HML
α, the promoter region of the α1 and α2 genes is nucleosome free and more nuclease sensitive in the repressed than in the transcribed locus. Mutations in genes essential for
HML
silencing disrupt the nucleosome array near HML-I but not in the vicinity of HML-E, which is closer to the telomere of chromosome III. At the promoter and the HO site, the structure of
HML
α in Sir protein and histone H4 N-terminal deletion mutants is identical to that of the transcriptionally active
MAT
α. The discontinuous chromatin structure of
HML
α contrasts with the continuous array of nucleosomes found at repressed a-cell-specific genes and the recombination enhancer. Punctuation at
HML
α may be necessary for higher-order structure or karyoskeleton interactions. The unique chromatin architecture of
HML
α may relate to the combined requirements of transcriptional repression and recombinational competence.
Publisher
American Society for Microbiology
Subject
Cell Biology,Molecular Biology
Cited by
114 articles.
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