SWI/SNF Stimulates the Formation of Disparate Activator-Nucleosome Complexes but Is Partially Redundant with Cooperative Binding*
- From the Department of Biochemistry and Molecular Biology and The Center for Gene Regulation, The Pennsylvania State University, University Park, Pennsylvania 16802-4500
Abstract
To investigate the potential mechanisms by which the SWI/SNF complex differentially regulates different genes we have tested whether transcription factors with diverse DNA binding domains were able to exploit nucleosome disruption by SWI/SNF. In addition to GAL4-VP16, the SWI/SNF complex stimulated nucleosome binding by the Zn2+ fingers of Sp1, the basic helix-loop-helix domain of USF, and the rel domain of NF-κB. In each case SWI/SNF action resulted in the formation of a stable factor-nucleosome complex that persisted after detachment of SWI/SNF from the nucleosome. Thus, stimulation of factor binding by SWI/SNF appears to be universal. The degree of SWI/SNF stimulation of nucleosome binding by a factor appears to be inversely related to the extent that binding is inhibited by the histone octamer. Cooperative binding of 5 GAL4-VP16 dimers to a 5-site nucleosome enhanced GAL4 binding relative to a single-site nucleosome, but this also reduced the degree of stimulation by SWI/SNF. The SWI/SNF complex increased the affinity of 5 GAL4-VP16 dimers for nucleosomes equal to that of DNA but no further. Similarly, multimerized NF-κB sites enhanced nucleosome binding by NF-κB and reduced the stimulatory effect of SWI/SNF. Thus, cooperative binding of factors to nucleosomes is partially redundant with the function of the SWI/SNF complex.
Footnotes
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↵* This work was supported by a grant from the National Institutes of Health (to J. L. W.), a Postdoctoral Fellowship and a Centennial Fellowship from the Canadian Medical Research Council (to J. C.), and a Leukemia Society Scholars Award (to J. L. W.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology and The Center for Gene Regulation, 306 Althouse Lab., The Pennsylvania State University, University Park, PA 16802-4500. Tel.: 814-863-8256; Fax: 814-863-0099; E-mail:JLW10{at}psu.edu.
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↵1 The abbreviations used are: bp, base pair(s); ySWI/SNF, yeast SWI/SNF.
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↵2 J. Côté and J. L. Workman, unpublished data.
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- Received December 11, 1996.
- Revision received February 19, 1997.
