Poirier Michael G, Oh Eugene, Tims Hannah S, Widom Jonathan
Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois, USA.
Nat Struct Mol Biol. 2009 Sep;16(9):938-44. doi: 10.1038/nsmb.1650. Epub 2009 Aug 23.
The packaging of eukaryotic DNA into chromatin sterically occludes polymerases, recombinases and repair enzymes. How chromatin structure changes to allow their actions is unknown. We constructed defined fluorescently labeled trinucleosome arrays, allowing analysis of chromatin conformational dynamics via fluorescence resonance energy transfer (FRET). The arrays undergo reversible Mg2+-dependent folding similar to that of longer arrays studied previously. We define two intermediate conformational states in the reversible folding of the nucleosome arrays and characterize the microscopic rate constants. Nucleosome arrays are highly dynamic even when compact, undergoing conformational fluctuations on timescales in the second to microsecond range. Compact states of the arrays allow binding to DNA within the central nucleosome via site exposure. Protein binding can also drive decompaction of the arrays. Thus, our results reveal multiple modes by which spontaneous chromatin fiber dynamics allow for the invasion and action of DNA-processing protein complexes.
真核生物的DNA包装成染色质在空间上会阻碍聚合酶、重组酶和修复酶的作用。染色质结构如何变化以允许它们发挥作用尚不清楚。我们构建了确定的荧光标记三核小体阵列，通过荧光共振能量转移（FRET）分析染色质构象动力学。这些阵列经历类似于先前研究的更长阵列的可逆Mg2+依赖性折叠。我们在核小体阵列的可逆折叠中定义了两个中间构象状态，并表征了微观速率常数。即使在紧密状态下，核小体阵列也具有高度动态性，在从秒到微秒的时间尺度上经历构象波动。阵列的紧密状态允许通过位点暴露与中央核小体内的DNA结合。蛋白质结合也可以驱动阵列的解压缩。因此，我们的结果揭示了自发染色质纤维动力学允许DNA加工蛋白复合物侵入和发挥作用的多种模式。
