Torque and dynamics of linking number relaxation in stretched supercoiled DNA
Torque and dynamics of linking number relaxation in stretched supercoiled DNA
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DOI：
10.1103/physreve.76.021926
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发表时间：
2007-08-01
影响因子：
2.4
通讯作者：
Marko, John F.
中科院分区：
文献类型：
--
作者：
Marko, John F.
在DNA的微力学研究中，超螺旋结构域常被用作恒定扭矩的来源。这些扭矩不容易测量，而是通常估计。在这里，共存的扩展和超螺旋的DNA结构域进行了分析，并提出了封闭形式的表达式的延伸和扭矩的力和连接数的依赖。当存在plectonemic和扩展DNA的共存结构域时，扭矩仅取决于力，而不依赖于连接数。然而，扭矩取决于力的方式比一个简单的幂律更复杂，涉及到扩展和plectonemic DNA的自由能。描述了一种简单的策略，用于测量的自由能的扩展和plectonemic DNA，而不参考特定的微观聚合物模型。应用该理论分析松弛的超螺旋酶，允许摩擦控制的旋转松弛的连接数。这样的酶必须显示由相等大小但相反方向的扭矩驱动的弛豫之间的对称性的破坏。
In micromechanical studies of DNA, plectonemically supercoiled domains are often used as sources of constant torque. These torques are not easily measured and are instead usually estimated. Here, coexisting extended and supercoiled DNA domains are analyzed, and closed-form expressions for the dependence of extension and torque on force and linking number are presented. When there are coexisting domains of plectonemic and extended DNA, the torque depends only on force, with no dependence on linking number. However, torque depends on force in a manner more complex than a simple power law, involving the free energy of the extended and plectonemic DNA. A simple strategy is described for measurement of the free energies of both extended and plectonemic DNA without reference to specific microscopic polymer models. Applications of the theory to analysis of relaxation of supercoiling by enzymes which permit friction-controlled rotational relaxation of linking number is also presented. Such enzymes must display a breaking of symmetry between relaxations driven by equal magnitude but opposite direction torques.