Ulanovsky L E, Trifonov E N
Cell Biophys. 1983 Dec;5(4):281-3. doi: 10.1007/BF02788626.
Winding DNA in a superhelix can be considered a process consisting of two smooth deformations: bending and twisting. The extra twist angle introduced by winding DNA into the nucleosomal superhelix is calculated by means of the Crick formula to be -0.5 degrees per base pair (bp). This is equivalent to a change of -0.15 +/- 0.015 bp in the DNA double-helical repeat. Free DNA in solution is known to have a helical repeat of 10.55 +/- 0.1 bp. On the other hand, a weighted average of various estimates of the DNA repeat in the nucleosome is 10.38 +/- 0.02. The difference happens to be perfectly accounted for by the superhelicity of the nucleosomal DNA. This implies that the latter is essentially nonconstrained .
将DNA缠绕成超螺旋可被视为一个由两种平滑变形组成的过程：弯曲和扭转。通过克里克公式计算得出，将DNA缠绕成核小体超螺旋所引入的额外扭转角度为每碱基对（bp）-0.5度。这相当于DNA双螺旋重复序列中-0.15±0.015 bp的变化。已知溶液中的游离DNA具有10.55±0.1 bp的螺旋重复序列。另一方面，核小体中DNA重复序列的各种估计值的加权平均值为10.38±0.02。这个差异恰好可以由核小体DNA的超螺旋度完美解释。这意味着后者本质上是不受约束的。
