TWIST AND WRITHING IN SHORT CIRCULAR DNAS ACCORDING TO 1ST-ORDER ELASTICITY
TWIST AND WRITHING IN SHORT CIRCULAR DNAS ACCORDING TO 1ST-ORDER ELASTICITY
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DOI：
10.1002/bip.360231004
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发表时间：
1984-01-01
期刊：
影响因子：
2.9
通讯作者：
LEBRET, M
中科院分区：
文献类型：
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作者：
LEBRET, M
研究了小于其持续长度的封闭DNA中扭曲和扭动的分布。在这种情况下，唯一的能量贡献是弹性的。我们积分了一个均匀轴对称杆的弹性方程，该杆具有不可变形的无限小的圆形横截面，具有无摩擦的反力，当没有或只有一个自接触时。在不存在自接触的情况下，杆的中心线绘制在圆环上。它绕着环形的旋转轴旋转v圈，绕着环形的核心旋转m圈。如果杆没有打结，整数ν等于1。我们证明了，如果没有自接触，则没有具有正泊松比的无限细杆在环形构象中是稳定的。然而，多叶玫瑰或玫瑰，只有一个多重自我接触，当它们的扭动不是太大时，实际上是稳定的。当整数m等于2时，我们有8字形构象。对于约束，圆屈曲成8字形构象，使得8字形构象和圆构象具有相同的能量。当弯扭弹性常数比A/C= 1.5时，该约束为1.845圈。对于相同的A/C值，当约束大于2.4圈时，8字形构象是不稳定的。修正引起的有限值的半径比，a/L，横截面的杆的长度，估计。例如，圆形构象和无限小翘曲圆都是特定β扭曲值的联立解。β =A/C（m2− ν2）½[1 +（νπa/L）2/2]。已经研究了乙锭与DNA的结合足够短以遵循一阶弹性。在表观平均约束约为0.6时发生屈曲。随着乙锭浓度的变化，DNA分子如何分布在8字形构象和圆形中已经被确定。
The distribution of twist and writhing in a closed DNA shorter than its persistence length is examined. In this case, the only energy contribution is elastic. We have in tegrated the equations of elasticity for a homogeneous axially symmetric rod of undeformable infinitely small circular cross section with frictionless reactions, when there is no or only one self‐contact. In the absence of self‐contacts, the central line of the rod is drawn on a toroid. It makes ν turns around the axis of revolution of the toroid andmturns around its core. The integer, ν, is equal to one if the rod is unknotted. We prove that no infinitely thin rod with a positive Poisson ratio is stable in a toroidal conformation if there is no self‐contact. However,m‐leafed roses or rosettes, with but one multiple self‐contact, are shown to actually be stable when their writhing is not too great. When the integer,m, is equal to two, we have figure‐8 conformations. Buckling of the circle into a figure‐8 conformation occurs for the constraint such that the figure‐8 and the circular conformations have the same energy. This constraint is 1.845 turns for a bending‐to‐twisting elastic constants ratio ofA/C= 1.5. For the same value ofA/C, the figure‐8 conformation is unstable for a constraint greater than 2.4 turns. Corrections caused by a finite value of the radius ratio,a/L, of the cross section to the length of the rod, are estimated. For instance, both the circular conformation and the infinitesimally warped circle are simultaneous solutions for particular values of the β twist. β =A/C(m2− ν2)½[1 + (νπa/L)2/2]. The binding of ethidium to DNAs short enough to follow first‐order elasticity has been studied. Buckling occurs at an apparent average constraint of about 0.6. How the DNA molecules are distributed in figure‐8 conformations and circles has been determined as the ethidium concentration is varied.