Control of nucleosome movement: to space or not to space nucleosomes?

A key feature of ATP-dependent chromatin remodeling complexes is how they control the ability of the complex to translocate along DNA within the context of a nucleosome. Although these complexes generally initiate DNA translocation near the dyad axis of the nucleosome, the progression and eventual termination is regulated in quite distinct ways. The best studied examples of these are the ISWI type which has strong extranucleosomal DNA dependent activity or the SWI/SNF type which has no linker DNA requirement. Recent data provide insights into the mechanism of regulation of DNA translocation by the ISWI type complexes and how the structure of the ISWI-nucleosome complex changes during chromatin remodeling.