Perturbation of nucleosome core structure by the SWI/SNF complex persists after its detachment, enhancing subsequent transcription factor binding

To investigate the mechanism of SWI/SNF action, we have analyzed the pathway by which SWI/SNF stimulates formation of transcription factor-bound nucleosome core complexes. We report here that the SWI/SNF complex binds directly to nucleosome cores and uses the energy of ATP hydrolysis to disrupt histone/DNA interactions, altering the preferred path of DNA bending around the histone octamer. This disruption occurs without dissociating the DNA from the surface of the histone octamer. ATP-dependent disruption of nucleosomal DNA by SWI/SNF generates an altered nucleosome core conformation that can persist for an extended period after detachment of the SWI/SNF complex. This disrupted conformation retains an enhanced affinity for the transcription factor GAL4-AH. Thus, ATP-dependent nucleosome core disruption and enhanced binding of the transcription factor can be temporally separated. These results indicate that SWI/SNF can act transiently in the remodeling of chromatin structure, even before interactions of transcription factors.