ISWI induces nucleosome sliding on nicked DNA

The ATPase ISWI is the molecular motor of several remodeling factors that t rigger nucleosome sliding in vitro. In search for the underlying mechanism, we found that unilateral binding of ISWI to a model nucleosome correlated with directional movement of the nucleosome toward the enzyme. It has been proposed that ISWI might loosen histone-DNA interactions through twisting D NA. However, nucleosome sliding assays on nicked DNA substrates suggest tha t propagation of altered twist is not involved. Surprisingly, nicks in the linker DNA in front of the nucleosome facilitate sliding. These data sugges t that the rate of nucleosome sliding is limited by a conformational change other than twisting, such as the formation of a short loop, of DNA at the entry into the nucleosome.