Nature Structural & Molecular Biology 13, 549 - 554 (2006)
Published online: 28 May 2006; | doi:10.1038/nsmb1102
Probing SWI/SNF remodeling of the nucleosome by unzipping single DNA moleculesAlla Shundrovsky1, Corey L Smith2, John T Lis3, Craig L Peterson2
& Michelle D Wang11
Cornell University, Department of Physics, Laboratory of Atomic and Solid State Physics, Ithaca, New York 14853, USA. 2
University of Massachusetts Medical School, Program in Molecular Medicine, Worcester, Massachusetts 01605, USA. 3
Cornell University, Department of Molecular Biology and Genetics, Ithaca, New York 14853, USA.
Correspondence should be addressed to Michelle D Wang mdw17@cornell.edu Chromatin-remodeling enzymes can overcome strong histone-DNA interactions within the nucleosome to regulate access of DNA-binding factors to the genetic code. By unzipping individual DNA duplexes, each containing a uniquely positioned nucleosome flanked by long segments of DNA, we directly probed histone-DNA interactions. The resulting disruption-force signatures were characteristic of the types and locations of interactions and allowed measurement of the positions of nucleosomes with 2.6-base-pair (bp) precision. Nucleosomes remodeled by yeast SWI/SNF were moved bidirectionally along the DNA, resulting in a continuous position distribution. The characteristic distance of motion was  28 bp per remodeling event, and each event occurred with a catalytic efficiency of 0.4 min-1 per nM SWI/SNF. Remodeled nucleosomes had essentially identical disruption signatures to those of unremodeled nucleosomes, indicating that their overall structure remained canonical. These results impose substantial constraints on the mechanism of SWI/SNF remodeling.
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