Dipartimento di Medicina Sperimentale, Università degli Studi di Milano-Bicocca, Via Cadore 48, Monza (MB) 20900, Italy.
Phys Rev Lett. 2012 Sep 14;109(11):118303. doi: 10.1103/PhysRevLett.109.118303. Epub 2012 Sep 13.
We use the "magnetic tweezers" technique to show the structural transitions that the DNA undergoes in the force-torsion space. In particular, we focus on the regions corresponding to negative supercoiling. These regions are characterized by the formation of the so-called denaturation bubbles, which play an essential role in the replication and transcription of DNA. We experimentally map the region of the force-torsion space where the denaturation takes place. We observe that large fluctuations in DNA extension occur at one of the boundaries of this region, i.e., when the formation of denaturation bubbles and of plectonemes compete. To describe the experiments, we introduce a suitable extension of the classical model. The model correctly describes the position of the denaturation regions, the transition boundaries, and the measured values of the DNA extension fluctuations.
我们使用“磁镊”技术来展示 DNA 在力-扭空间中经历的结构转变。特别是，我们关注对应于负超螺旋的区域。这些区域的特点是形成所谓的变性泡，它们在 DNA 的复制和转录中起着至关重要的作用。我们通过实验绘制了发生变性的力-扭空间区域。我们观察到，在该区域的一个边界处，DNA 延伸发生了较大的波动，即当变性泡和扭结的形成竞争时。为了描述实验，我们引入了经典模型的一个合适扩展。该模型正确地描述了变性区域的位置、转变边界以及测量得到的 DNA 延伸波动值。
