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Molecular and Cellular Biology, October 2008, p. 6010-6021, Vol. 28, No. 19
0270-7306/08/$08.00+0 doi:10.1128/MCB.00693-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Bei Zhang,1,4,
Rachel Horowitz-Scherer,2
Jim Persinger,1
Christopher L. Woodcock,2
Craig L. Peterson,3 and
Blaine Bartholomew1*
Department of Biochemistry and Molecular Biology, Southern Illinois University, Carbondale, Illinois 62901-4413,1 Department of Biology, University of Massachusetts, Amherst, Massachusetts 01003,2 Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605,3 Department of Biology, Thomas University, 1501 Millpond Road, Thomasville, Georgia 317924
Received 28 April 2008/ Returned for modification 22 May 2008/ Accepted 15 July 2008
The SWI/SNF complex disrupts and mobilizes chromatin in an ATP-dependent manner. SWI/SNF interactions with nucleosomes were mapped by DNA footprinting and site-directed DNA and protein cross-linking when SWI/SNF was recruited by a transcription activator. SWI/SNF was found by DNA footprinting to contact tightly around one gyre of DNA spanning
50 bp from the nucleosomal entry site to near the dyad axis. The DNA footprint is consistent with nucleosomes binding to an asymmetric trough of SWI/SNF that was revealed by the improved imaging of free SWI/SNF. The DNA site-directed cross-linking revealed that the catalytic subunit Swi2/Snf2 is associated with nucleosomes two helical turns from the dyad axis and that the Snf6 subunit is proximal to the transcription factor recruiting SWI/SNF. The highly conserved Snf5 subunit associates with the histone octamer and not with nucleosomal DNA. The model of the binding trough of SWI/SNF illustrates how nucleosomal DNA can be mobilized while SWI/SNF remains bound.
Published ahead of print on 21 July 2008.
M.L.D. and B.Z. have equally contributed to this work.
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