Hirai M, Niimura N, Zama M, Mita K, Ichimura S, Tokunaga F, Ishikawa Y
Kanagawa Institute of Technology, Atsugi, Japan.
Biochemistry. 1988 Oct 4;27(20):7924-31. doi: 10.1021/bi00420a051.
The structural behavior of the nucleosome core particles in the range of solvent Na+ concentration from 10.45 to 0.45 mM has been studied by small-angle neutron and synchroton radiation X-ray scattering, sedimentation, atomic absorption spectroscopy, density measurements, and circular dichroism. With decreasing salt concentration, the appearance of a scattering peak that is assignable to interparticle interactions, an intraparticle structural transition, a decrease in the sedimentation velocity of the particle, and a release of bound Na+ ions from the particle are all observed concurrently when the ratio of solvent Na+ ions per particle is below approximately 1000. These observations are interpreted to indicate that a release of bound Na+ ions from the particle brings about structural rearrangements and weakens the electrostatic shielding of the particle, and this introduces long-range repulsive ordering of the particle in low-salt solution. Analyses of the scattering data indicate that the rearrangement within the core particle in low-salt solution is slight, changing the particle's shape slightly from cylindrical to a more spherical form by moving the center of the mass of the DNA somewhat inward with accompanying small decreases in the radii of gyration of both the DNA and the histones.
通过小角中子散射和同步辐射X射线散射、沉降、原子吸收光谱、密度测量以及圆二色性研究了核小体核心颗粒在溶剂Na⁺浓度从10.45 mM到0.45 mM范围内的结构行为。随着盐浓度降低，当每个颗粒的溶剂Na⁺离子比率低于约1000时，可归因于颗粒间相互作用的散射峰的出现、颗粒内结构转变、颗粒沉降速度的降低以及颗粒中结合的Na⁺离子的释放会同时被观察到。这些观察结果被解释为表明颗粒中结合的Na⁺离子的释放导致结构重排并削弱了颗粒的静电屏蔽，这在低盐溶液中引入了颗粒的长程排斥有序排列。散射数据分析表明，低盐溶液中核心颗粒内的重排轻微，通过将DNA的质心稍微向内移动，同时DNA和组蛋白的回转半径略有减小，使颗粒形状从圆柱形略微变为更球形。
