Sequence-specific positioning of nucleosomes over the steroid-inducible MMTV promoter.
We have investigated chromatin organization over the MMTV LTR, a promoter regulated by steroid hormones. The studies were performed on cell lines containing BPV-based episomal constructs. Nucleosome positioning was determined by localization of sites sensitive to the enzyme micrococcal nuclease, or to the chemical MPE-Fe(II). Experiments with both reagents indicate that nucleosomes are specifically positioned in MMTV LTR chromatin. In the absence of hormone a regular cutting pattern is obtained, with cleavage sites at +136, -60, -250, -444, -651, -826 and -1019 relative to the Cap site. In the presence of hormone the cutting pattern is unchanged, except for a region between -60 and -250 that becomes hypersensitive to MPE-Fe(II). This region contains the DNA sequences to which steroid receptor complexes bind during transcriptional activation. Our results indicate that this region is associated in chromatin from uninduced cells with a macromolecular complex (probably a nucleosome core), and this complex is displaced (or modified) upon binding of activated receptor.
Richard-Foy
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Hormone Action and Oncogenesis Section, National Cancer Institute, Bethesda, MD 20892.
Hager
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D001483:Base Sequence; D002460:Cell Line; D002843:Chromatin / Q000502:physiology; D004262:DNA Restriction Enzymes; D003907:Dexamethasone / Q000494:pharmacology*; D005784:Gene Amplification; D005809:Genes, Regulator / Q000187:drug effects; D005814:Genes, Viral / Q000187:drug effects; D008324:Mammary Tumor Virus, Mouse / Q000187:drug effects / Q000235:genetics*; D009707:Nucleosomes / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000187:drug effects
D002843:Chromatin; D009707:Nucleosomes; D003907:Dexamethasone; D004262:DNA Restriction Enzymes