Feigon J, Kearns D R
Nucleic Acids Res. 1979;6(6):2327-37. doi: 10.1093/nar/6.6.2327.
In this study 1H NMR has been used to investigate the conformational state of DNA in nucleosome core particles. The nucleosome core particles exhibit partially resolved low field (10-15 ppm) spectra due to imino protons in Watson-Crick base pairs (one resonance per GC or AT base pair). To a first approximation, the spectrum is virtually identical with that of protein-free 140 base pair DNA, and from this observation we draw two important conclusions: (i) Since the low field spectra of DNA are known to be sensitive to conformation, the conformation of DNA in the core particles is essentially the same as that of free DNA (presumably B-form), (ii) since kinks occurring at a frequency at 1 in 10 or 1 in 20 base pairs would result in a core particle spectrum different from that of free DNA we find no NMR evidence supporting either the Crick-Klug or the Sobell models for kinking DNA around the core histones. Linewidth considerations indicate that the rotational correlation time for the core particles is approximately 1.5 X 10(-7) sec, whereas the end-over-end tumbling time of the free 140 base pair DNA is 3 X 10(-7) sec.
在本研究中，利用核磁共振氢谱（1H NMR）来研究核小体核心颗粒中DNA的构象状态。由于沃森-克里克碱基对中的亚氨基质子（每个GC或AT碱基对有一个共振峰），核小体核心颗粒呈现出部分分辨的低场（10 - 15 ppm）光谱。初步估算，该光谱与无蛋白的140碱基对DNA的光谱几乎相同，基于这一观察结果我们得出两个重要结论：（i）由于已知DNA的低场光谱对构象敏感，核心颗粒中DNA的构象与游离DNA的构象基本相同（推测为B型），（ii）由于每10个或20个碱基对中出现一次的扭结会导致核心颗粒光谱与游离DNA的光谱不同，我们未发现核磁共振证据支持围绕核心组蛋白扭结DNA的克里克-克鲁格模型或索贝尔模型。线宽考量表明，核心颗粒的旋转相关时间约为1.5×10^(-7) 秒，而游离的140碱基对DNA的端到端翻滚时间为3×10^(-7) 秒。
