Grosberg A Iu, Zhestkov A V
Mol Biol (Mosk). 1985 Jul-Aug;19(4):1153-6.
The influence of torsional elasticity of the double helix on compactization and structure of circular DNA in a compact form is studied in the case when the compact (globular) particle has a torus shape. For closed circular DNA the topological invariant, linking number of two strains, yields strict connection between conformation of double helix, considered as a unifilar homopolymer, and elastic energy of torsional twisting. The contribution of torsional elasticity to free energy of the toruslike globule is calculated. This contribution is shown to be proportional to the square of superturn's density. Torsional elasticity decreases the equilibrium radius of the toruslike globule formed by circular DNA in comparison with the case of linear DNA. Closure of linear DNA into a ring widens the stability range of the relatively short DNA compact form and tightens it for long DNA.
在紧密（球状）颗粒呈圆环形状的情况下，研究了双螺旋的扭转弹性对呈紧密形式的环状DNA的压缩和结构的影响。对于闭环环状DNA，拓扑不变量——两条链的连环数，在将双螺旋视为单链均聚物的构象与扭转扭曲的弹性能之间产生了严格的关联。计算了扭转弹性对类圆环小球自由能的贡献。结果表明，这一贡献与超螺旋密度的平方成正比。与线性DNA的情况相比，扭转弹性减小了由环状DNA形成的类圆环小球的平衡半径。将线性DNA闭环会拓宽相对较短DNA紧密形式的稳定性范围，并使长DNA的紧密形式更加紧密。
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