ISWI is an ATP-dependent nucleosome remodeling factor

The ATPase ISWI is a subunit of several distinct nucleosome remodeling comp lexes that increase the accessibility of DNA in chromatin. We found that th e isolated ISWI protein itself was able to carry out nucleosome remodeling, nucleosome rearrangement, and chromatin assembly reactions. The ATPase act ivity of ISWI was stimulated by nucleosomes but not by free DNA or free his tones, indicating that ISWI recognizes a specific structural feature of nuc leosomes. Nucleosome remodeling, therefore, does not require a functional i nteraction between ISWI and the other subunits of ISWI complexes. The role of proteins associated with ISWI may be to regulate the activity of the rem odeling engine or to define the physiological context within which a nucleo some remodeling reaction occurs.