Wall G, Varga-Weisz P D, Sandaltzopoulos R, Becker P B
European Molecular Biology Laboratory, Gene Expression Programme, Heidelberg, Germany.
EMBO J. 1995 Apr 18;14(8):1727-36. doi: 10.1002/j.1460-2075.1995.tb07162.x.
The chromatin structure at the Drosophila hsp26 promoter in vivo is characterized by two DNase I-hypersensitive (DH) sites harboring regulatory elements. Proximal and distal DH sites are separated by a positioned nucleosome. To study the contribution of transcription factors to the establishment of this specific chromatin configuration we assembled nucleosomes on the hsp26 promoter using a cell-free reconstitution system derived from fly embryos. Both DH sites were readily reconstituted from extract components. They were separated by a nucleosome which was less strictly positioned than its in vivo counterpart. The interactions of GAGA factor and heat shock factor with their binding sites in chromatin occurred in two modes. Their interaction with binding sites in the nucleosome-free regions did not require ATP. In the presence of ATP both factors interacted also with nucleosomal binding sites, causing nucleosome rearrangements and a refinement of nucleosome positions. While chromatin remodeling upon transcription factor interaction has previously been interpreted to involve nucleosome disruption, the data suggest energy-dependent nucleosome sliding as main principle of chromatin reorganization.
果蝇hsp26启动子在体内的染色质结构的特征是有两个含有调控元件的DNA酶I超敏（DH）位点。近端和远端DH位点被一个定位核小体隔开。为了研究转录因子对这种特定染色质构型建立的贡献，我们使用从果蝇胚胎衍生的无细胞重组系统在hsp26启动子上组装核小体。两个DH位点都很容易从提取物成分中重组出来。它们被一个定位不如体内对应物严格的核小体隔开。GAGA因子和热休克因子与其在染色质中的结合位点的相互作用以两种模式发生。它们与无核小体区域中结合位点的相互作用不需要ATP。在ATP存在的情况下，这两种因子也与核小体结合位点相互作用，导致核小体重排和核小体位置的细化。虽然转录因子相互作用后的染色质重塑以前被解释为涉及核小体破坏，但数据表明能量依赖的核小体滑动是染色质重组的主要原则。
