Mergell Boris, Everaers Ralf, Schiessel Helmut
Max-Planck-Institut für Polymerforschung, Postfach 3148, D-55021 Mainz, Germany.
Phys Rev E Stat Nonlin Soft Matter Phys. 2004 Jul;70(1 Pt 1):011915. doi: 10.1103/PhysRevE.70.011915. Epub 2004 Jul 29.
We use Monte Carlo simulations to study attractive and excluded volume interactions between nucleosome core particles in 30-nm chromatin fibers. The nucleosomes are treated as disklike objects having an excluded volume and short-range attraction modeled by a variant of the Gay-Berne potential. The nucleosomes are connected via bendable and twistable linker DNA in the crossed linker fashion. We investigate the influence of the nucleosomal excluded volume on the stiffness of the fiber. For parameter values that correspond to chicken erythrocyte chromatin, we find that the persistence length is governed to a large extent by that excluded volume whereas the soft linker backbone elasticity plays only a minor role. We further find that internucleosomal attraction can induce the formation of hairpin configurations. Tension-induced opening of such configurations into straight fibers manifests itself in a quasiplateau in the force-extension curve that resembles results from recent micromanipulation experiments. Such hairpins may play a role in the formation of higher-order structures in chromosomes like chromonema fibers.
我们使用蒙特卡罗模拟来研究30纳米染色质纤维中核小体核心颗粒之间的吸引相互作用和排除体积相互作用。核小体被视为具有排除体积的盘状物体，并通过盖伊 - 伯恩势的变体对短程吸引力进行建模。核小体通过可弯曲和可扭转的连接子DNA以交叉连接子的方式相连。我们研究了核小体排除体积对纤维刚度的影响。对于与鸡红细胞染色质相对应的参数值，我们发现持久长度在很大程度上由该排除体积决定，而柔软的连接子主干弹性仅起次要作用。我们还发现核小体间的吸引力可诱导发夹构型的形成。张力诱导此类构型打开形成直纤维，这在力 - 伸长曲线中表现为准平台，类似于近期微操纵实验的结果。此类发夹可能在染色体中高阶结构如染色线纤维的形成中发挥作用。
