be consistent with the highly tissue-specific nature of deoxyribonuclease (DNase) sensitivity over the genome (118). Finally, we would expect that the effect of TopoII would not be seen in an in vitro transcription reaction using nucleosomal templates. Indeed, this is the case because the minimal set of BAF subunits necessary for in vitro transcription does not include TopoII, and the subunit to which TopoII binds, BAF250, is not necessary for transcription on nucleosomal templates. In yeast, TopoII function was shown to require nucleosome-free DNA, and the loss of the snf5 gene interfered with the binding of TopoIIa (119).
