Edayathumangalam Rajeswari S, Weyermann Philipp, Dervan Peter B, Gottesfeld Joel M, Luger Karolin
Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO 80523-1870, USA.
J Mol Biol. 2005 Jan 7;345(1):103-14. doi: 10.1016/j.jmb.2004.10.012.
The 2.0 A crystal structure of a nucleosome core particle in complex with a bivalent pyrrole-imidazole polyamide reveals that this "clamp" effectively crossbraces the two gyres of the DNA superhelix, thereby stabilizing the nucleosome against dissociation. Using X-ray crystallography and footprinting techniques, we show that the clamp preferentially binds nucleosomes over free DNA, and that nucleosomal DNA exists as a mixture of multiple twist-defect intermediates in solution. The nucleosomes exist in one of two different conformations in various crystal structures that trap twist-defect intermediates, even on a strong positioning sequence. Evidence has been obtained supporting the existence of twist-defect states in nucleosomal DNA in solution that are similar to those obtained in crystal structures. Our results also substantiate the idea that twist diffusion may represent an important means of altering the accessibility of nucleosomal DNA both in the presence and in the absence of ATP-dependent chromatin-remodelling enzymes.
一种与二价吡咯 - 咪唑聚酰胺复合的核小体核心颗粒的2.0埃晶体结构表明，这种“夹子”有效地交叉支撑了DNA超螺旋的两个螺旋，从而稳定了核小体使其不易解离。利用X射线晶体学和足迹技术，我们表明该夹子优先结合核小体而非游离DNA，并且核小体DNA在溶液中以多种扭曲缺陷中间体的混合物形式存在。在各种捕获扭曲缺陷中间体的晶体结构中，核小体以两种不同构象之一存在，即使在强定位序列上也是如此。已经获得证据支持溶液中核小体DNA中存在与晶体结构中获得的类似的扭曲缺陷状态。我们的结果还证实了这样一种观点，即扭曲扩散可能是在存在和不存在ATP依赖的染色质重塑酶的情况下改变核小体DNA可及性的重要手段。
