The SWI/SNF Complex Creates Loop Domains in DNA and Polynucleosome Arrays and Can Disrupt DNA-Histone Contacts within These Domains

To understand the mechanisms by which the chromatin-remodeling SWI/SNF complex interacts with DNA and alters nucleosome organization, we have imaged the SWI/SNF complex with both naked DNA and nucleosomal arrays by using energy-filtered microscopy. By making ATP-independent contacts with DNA at multiple sites on its surface, SWI/SNF creates loops, bringing otherwise-distant sites into close proximity. In the presence of ATP, SWI/SNF action leads to the disruption of nucleosomes within domains that appear to be topologically constrained by the complex. The data indicate that the action of one SWI/SNF complex on an array of nucleosomes can lead to the formation of a region where multiple nucleosomes are disrupted. Importantly, nucleosome disruption by SWI/SNF results in a loss of DNA content from the nucleosomes. This indicates a mechanism by which SWI/SNF unwraps part of the nucleosomal DNA.