Kabakçioğlu A, Orlandini E, Mukamel D
Department of Physics, Koç University, Sariyer, 34450 Istanbul, Turkey.
Phys Rev E Stat Nonlin Soft Matter Phys. 2009 Jul;80(1 Pt 1):010903. doi: 10.1103/PhysRevE.80.010903. Epub 2009 Jul 10.
We generalize the Poland-Scheraga model to the case of a circular DNA, taking into account the twisting of the two strains around each other. Guided by recent single-molecule experiments on DNA strands, we assume that the torsional stress induced by denaturation enforces the formation of supercoils whose writhe absorbs the linking number expelled by the loops. Our model predicts that when the entropy parameter of a loop satisfies c<or=2, denaturation transition does not take place. On the other hand, for c>2, a first-order denaturation transition is consistent with our model and may take place in the actual system, as in the case with no supercoils. These results are in contrast with other treatments of circular DNA melting where denaturation is assumed to be accompanied by an increase in twist rather than writhe on the bound segments.
我们将波兰-谢拉加模型推广到环状DNA的情况，考虑了两条链相互缠绕的扭曲情况。受近期DNA链单分子实验的启发，我们假设变性诱导的扭转应力促使超螺旋形成，其缠绕数吸收由环排出的连接数。我们的模型预测，当一个环的熵参数满足c≤2时，不会发生变性转变。另一方面，对于c>2，一级变性转变与我们的模型一致，并且可能在实际系统中发生，就像没有超螺旋的情况一样。这些结果与环状DNA解链的其他处理方法形成对比，在其他处理中，假设变性伴随着结合片段上扭转的增加而不是缠绕的增加。
