SWI/SNF unwraps,slides, and rewraps the nucleosome

The structure of the SWI/SNF-remodeled nucleosome was characterized with single base-pair resolution by mapping the contacts of specific histone fold residues with nucleosomal DNA. We demonstrate that SWI/SNF peels up to 50 bp of DNA from the edge of the nucleosome, translocates the histone octamer beyond the DNA ends via a DNA bulge propagation mechanism, and promotes the formation of an intramolecular DNA loop between the nucleosomal entry and exit sites. This stable altered nucleosome conformation also exhibits alterations in the distance between contacts of specific histone residues with DNA and higher electrophoretic and sedimentation mobility, consistent with a more compact molecular shape. SWI/SNF converts a nucleosome to the altered state in less than 1 s, hydrolyzing fewer than 10 ATPs per event.