Leibniz Institute of Polymer Research Dresden, Dresden, Germany.
Biophys J. 2011 Jun 8;100(11):2539-47. doi: 10.1016/j.bpj.2011.03.053.
We study the segregation of two long chains from parallel but randomly twisted start conformations under good solvent conditions using Monte Carlo simulations to mimic chromatin segregation after replication in eukaryotic cells in the end of prophase. To measure the segregation process, we consider the center-of-mass separation between the two chains and the average square distance between the monomers which were connected before segregation starts. We argue that segregation is dominated by free diffusion of the chains, assuming that untwisting can be achieved by Rouse-like fluctuations on the length scale of a twisted loop. Using scaling analysis, we find that chain dynamics is in very good agreement with the free diffusion hypothesis, and segregation dynamics follows this scaling nearly. Long chains, however, show retardation effects that can be described by a new (to us) dynamical exponent, which is slightly larger than the dynamical exponent for Rouse-like diffusion. Our results indicate that nearly free diffusion of chains during a timescale of a few Rouse-times can lead to segregation of chains. A main obstacle during segregation by free diffusion is random twists between daughter strands. We have calculated the number of twists formed by the daughter strands in the start conformations, which turns out to be rather low and increases only with the square-root of the chain length.
我们使用蒙特卡罗模拟研究了在良好溶剂条件下两条长链从平行但随机扭曲的起始构象中的分离，以模拟真核细胞末期复制后染色质的分离。为了测量分离过程，我们考虑了两条链的质心分离和在分离开始之前连接的单体的平均平方距离。我们认为，假设解扭可以通过扭结环长度尺度上的类似 Rouse 的涨落来实现，那么分离主要由链的自由扩散主导。通过标度分析，我们发现链动力学与自由扩散假设非常吻合，并且分离动力学几乎遵循这种标度。然而，长链表现出延迟效应，可用一个新的（对我们来说）动力学指数来描述，该指数略大于类似 Rouse 的扩散的动力学指数。我们的结果表明，在几个 Rouse 时间的时间尺度内，链的几乎自由扩散可以导致链的分离。自由扩散过程中分离的主要障碍是子链之间的随机扭曲。我们已经计算了起始构象中形成的子链的扭曲数量，结果发现扭曲数量相当低，并且仅随链长的平方根增加。
