ySWI/SNF complex belongs to a family of enzymes that use the energy of ATP
hydrolysis to remodel chromatin structure. Here we examine the role of DNA
topology in the mechanism of ySWI/SNF remodeling. We find that the ability
of ySWI/SNF to enhance accessibility of nucleosomal DNA is nearly eliminate
d when DNA topology is constrained in small circular nucleosomal arrays and
that this inhibition can be alleviated by topoisomerases. Furthermore, we
demonstrate that remodeling of these substrates does not require dramatic h
istone octamer movements or displacement. Our results suggest a model in wh
ich ySWI/SNF remodels nucleosomes by using the energy of ATP hydrolysis to
drive local changes in DNA twist.