text: A number of distinct reactions are associated with the term ATP-dependent chromatin remodeling. Remodeling enzymes have been shown to slide nucleosomes along DNA, disrupt histone-DNA contacts to the extent of destabilizing the H2A/H2B dimer and to generate negative superhelical torsion in DNA and chromatin. Recently, the Swr1 remodeling enzyme has been shown to introduce the variant histone H2A.Z into nucleosomes. At present, it is not clear if all of these represent distinct reactions or merely alternative outcomes of a common mechanism. What is shared between all, and indeed the hallmark of ATP-dependent chromatin remodeling, is that they all result in altered DNA accessibility.
  Studies looking at gene activation in vivo and, more astonishingly, remodeling in vitro have revealed that chromatin remodeling events and transcription-factor binding are cyclical and periodic in nature. While the consequences of this for the reaction mechanism of chromatin remodeling are not known, the dynamic nature of the system may allow it to respond faster to external stimuli. A recent study indicates that nucleosome positions change significantly during mouse embryonic stem cell development, and these changes are related to binding of developmental transcription factors.