Mol Cell Biol, June 1998, p. 3633-3644, Vol. 18, No. 6
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-5055
Received 22 January 1998/Returned for modification 2 March 1998/Accepted 6 March 1998
Stimulation of the mouse mammary tumor virus with steroids results
in the generation of a DNase I-hypersensitive region (HSR) spanning the
hormone responsive element (HRE) in the long terminal repeat.
Restriction enzymes were used to characterize the accessibility of
various sites within the HSR of mouse mammary tumor virus long terminal
repeat-reporter constructions in four different cell lines. The
glucocorticoid-dependent HSR was found to span minimally 187 bases, a
stretch of DNA longer than that associated with histones in the core
particle. Although the 5'-most receptor binding site within the HRE is
downstream of
190, hypersensitive sites were found further upstream
to at least
295. The relationship in the accessibility between pairs
of sites in the vicinity of the HSR was further examined in one cell
line by a two-enzyme restriction access assay. In the uninduced state,
the accessibilities at these sites were found to be independent of each
other. In contrast, when stimulated with hormone, the accessibilities
at these sites were observed to become linked. That is, once a distinct
promoter was activated, all of the sites within the HSR of that
molecule became accessible. The HSR formed along an invariant stretch
of DNA sequence despite the multiplicity of nucleosome frames in the
nucleosome B region, where the HRE is located. The results indicate
that the macroscopic length of the HSR does not arise from core
length-remodeling events in molecules containing Nuc-B in alternative
positions.
Present address: Department of Biology, Johns Hopkins University,
Baltimore, MD 21218.
Present address: Zeneca Laboratories, Macclesfield, United
Kingdom.
§
Present address: Department of Biochemistry and Molecular Biology,
Pennsylvania State University, University Park, PA 16802-4500.
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