Cowman M K, Fasman G D
Proc Natl Acad Sci U S A. 1978 Oct;75(10):4759-63. doi: 10.1073/pnas.75.10.4759.
Mononucleosomes were isolated from micrococcal nuclease digests of chicken erythrocyte nuclei. The circular dichroism properties of mononucleosome preparations, differing in average DNA length and in H1 and H5 content, demonstrate that the spectrum of chromatin is due only to the complete structure of its repeating subunits. The nucleoprotein spectra are all altered relative to protein-free DNA by the emergence of a single negative band at 275 nm, similar to the band observed for psi DNA. The intensity of the psi-type band depends on the proportion of DNA condensed in a specific manner. The psi-type band is proposed to be due to the compact DNA tertiary structure; i.e., the manner in which the DNA is wound around the histone core allowing interactions between adjacent turns of the superhelix. This interpretation attributes changes and variability in nucleoprotein circular dichroism spectra under different experimental conditions to alterations in DNA tertiary structure rather than secondary structure.
单核小体是从鸡红细胞核的微球菌核酸酶消化物中分离出来的。平均DNA长度以及H1和H5含量不同的单核小体制剂的圆二色性特性表明，染色质的光谱仅归因于其重复亚基的完整结构。相对于无蛋白质的DNA，核蛋白光谱都因在275nm处出现单一负带而发生改变，这与ψDNA观察到的带相似。ψ型带的强度取决于以特定方式浓缩的DNA比例。有人提出，ψ型带是由于紧密的DNA三级结构所致；也就是说，DNA缠绕在组蛋白核心周围的方式允许超螺旋相邻圈之间相互作用。这种解释将不同实验条件下核蛋白圆二色性光谱的变化和变异性归因于DNA三级结构的改变，而非二级结构的改变。
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