TORSIONAL RIGIDITY OF DNA AND LENGTH DEPENDENCE OF THE FREE-ENERGY OF DNA SUPERCOILING
TORSIONAL RIGIDITY OF DNA AND LENGTH DEPENDENCE OF THE FREE-ENERGY OF DNA SUPERCOILING
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DOI：
10.1016/0022-2836(84)90404-2
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发表时间：
1984-01-01
影响因子：
5.6
通讯作者：
WANG, JC
中科院分区：
文献类型：
--
作者：
HOROWITZ, DS;WANG, JC
通过分析仅在连接数上不同的[质粒] DNA拓扑异构体的玻尔兹曼布居，DNA超螺旋的连接数α。的DNA环小至200个碱基对（bp）的长度。所有的实验数据可以通过关系Δ G τ拟合。= K（α-.阿尔法度）2，是α。℃下是在给定的一组条件下给定DNA的常数，K是DNA长度依赖性比例常数。对于长度N大于2000 bp的DNA环，K与N成反比，并且产物NK在1150 RT附近几乎是常数。BP.对于小于2000 bp的环，NK随着N的降低而稳定地增加;对于200 bp的环，NK为3900 RT。BP.当N减少时NK的增加可以解释为扭动数的波动对α的平衡分布的贡献减少的结果。假设对于200 bp大小的DNA环，扭转贡献接近于零，则计算出DNA双螺旋的扭转刚度为2.9 × 10 - 4。10-10尔格厘米。此外，小圆圈的大K值允许精确计算DNA的螺旋重复。对于210 bp的环，重复测量为10.54 bp。
By analyzing the Boltzmann populations of [plasmid] DNA topoisomers that differ only in their linking numbers, the dependence of the free energy .DELTA.G.tau. of DNA supercoiling on the linking number .alpha. was determined for DNA rings as small as 200 base-pairs (bp) in length. All experimental data can be fitted by the relation .DELTA.G.tau. = K(.alpha.-.alpha..degree.)2, were .alpha..degree. is a constant for a given DNA at a given set of conditions and K is a DNA length-dependent proportionality constant. For DNA rings with length N larger than 2000 bp, K is inversely proportional to N and the product NK is nearly a constant around 1150 RT .cntdot. bp. For rings smaller than 2000 bp NK increases steadily with decreasing N; for a 200 bp ring NK is 3900 RT .cntdot. bp. The increase in NK when N decreases can be interpreted as a result of the decrease in the contribution of the fluctuation in the writhing number to the equilibrium distribution in .alpha.. Assuming that the writhing contribution approaches zero for DNA rings 200 bp in size, the torsional rigidity of the DNA double helix is calculated to be 2.9 .times. 10-10 erg cm. In addition, the large value of K for the small circles allows precise calculation of the helical repeat of DNA. For the 210 bp rings, the repeat is measured to be 10.54 bp.