Hjelm R P, Kneale G G, Sauau P, Baldwin J P, Bradbury E M, Ibel K
Cell. 1977 Jan;10(1):139-51. doi: 10.1016/0092-8674(77)90148-9.
Neutron scattering studies have been performed on dilute solutions of the fundamental subunit of chromatin, the nucleosome. The subunits contain approximately 195 base paris (bp) of DNA and histones H2A, H2B, H3, and H4. Measurements of the small angle scattering curves in various H2O/D2O solvents allow the contrast dependence of the radius of gyration of the subunits to be examined and give the mean scattering density of the particle. Further application of contrast variation to the higher angle scatter curves allows the contributions from the shape and internal structure of the subunits to be analyzed separately. From these results, we are able to propose a spherically averaged structure with most of the histones closely packed into a core of radius 3.2 nm surrounded by a loosely packed DNA-rich shell of 2.0 nm thickness resulting in a particle of 5.2 nm average radius. Model calculations for ellipsoids show that the outer shape of the subunit must have an axial ratio between 0.5 and 1.4 but is probably best described by more spherical particle. These results are correlated with the diffraction from chromatin films to provide an explanation for some of the diffraction rings.
已对染色质的基本亚基核小体的稀溶液进行了中子散射研究。这些亚基包含约195个碱基对（bp）的DNA以及组蛋白H2A、H2B、H3和H4。在各种H₂O/D₂O溶剂中测量小角散射曲线，可研究亚基回转半径的对比度依赖性，并得出粒子的平均散射密度。将对比度变化进一步应用于高角度散射曲线，可以分别分析亚基形状和内部结构的贡献。根据这些结果，我们能够提出一种球形平均结构，其中大部分组蛋白紧密堆积成半径为3.2 nm的核心，周围是厚度为2.0 nm的富含DNA的松散堆积壳层，从而形成平均半径为5.2 nm的粒子。椭球体的模型计算表明，亚基的外形轴向比必须在0.5到1.4之间，但可能用更接近球形的粒子来描述最为合适。这些结果与染色质膜的衍射相关，以解释一些衍射环。
