Figure 5.

Models for nucleosome remodelling by ISWI. (A) Power stroke model. First, the ATPase engine of ISWI translocates 7 bp of DNA. The ATPase and HSS domains then undergo a power stroke that exerts force on the HSS domains. The power stroke pulls 3 bp of flanking DNA into the nucleosome. Hypothetical force-transducing elements are coloured red. (B) Ratchet model. As in A, the ATPase engine translocates 7 bp. This translocation strains the structure of the nucleosome, in particular the DNA delimitated by the ATPase and HSS domains (red). When the strain on the nucleosome structure becomes too large, 3 bp of DNA ratchet into the nucleosome. No direct coordination between the HSS and ATPase domain is required for this mechanism and flexible linkage between individual domains (curved lines) does not affect remodelling. Histones are light blue; DNA is grey.