The transcriptionally-active MMTV promoter is depleted of histone H1

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Abstract
We have used an ultraviolet light cross-linking and immunoadsorption assay to demonstrate that histones HI and H2B are bound to the repressed MMTV promoter. (Hormone activation results in reduced Ml content with little or no change in H2B. High resolution analysis of the glucocorticoid-inducible DNasel hypersensitive region demonstrates an NF-1 footprint as well as specific sites of enhanced cleavage on nucleosome B and in the nucleosome B/nucleosome A linker. These results are consistent with a model in which binding of the glucocorticoid receptor to glucocoirticoid regulatory elements on the surface of nucleosome B induces a chromatin transition that is necessary for transcription factor (NF-1 and TFDID) recruitment to the MMTV promoter. We hypothesize that association of histone H1 with important cis-elements on the promoter masks these sites, and glucocorticoid-induced displacement of H1 is necessary to expose factor binding sites at the 3' edge of nucleosome B, in the nucleosome B/nucleosome A linker and at the 5' edge of nucleosome A.