Howard Hughes Medical Institute, Cornell University, Ithaca, New York 14853, USA.
Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA.
Phys Rev Lett. 2021 Jul 9;127(2):028101. doi: 10.1103/PhysRevLett.127.028101.
DNA torsional elastic properties play a crucial role in DNA structure, topology, and the regulation of motor protein progression. However, direct measurements of these parameters are experimentally challenging. Here, we present a constant-extension method integrated into an angular optical trap to directly measure torque during DNA supercoiling. We measured the twist persistence length of extended DNA to be 22 nm under an extremely low force (∼0.02 pN) and the twist persistence length of plectonemic DNA to be 24 nm. In addition, we implemented a rigorous data analysis scheme that bridged our measurements with existing theoretical models of DNA torsional behavior. This comprehensive set of torsional parameters demonstrates that at least 20% of DNA supercoiling is partitioned into twist for both extended DNA and plectonemic DNA. This work provides a new experimental methodology, as well as an analytical and interpretational framework, which will enable, expand, and enhance future studies of DNA torsional properties.
DNA 的扭转弹性特性在 DNA 结构、拓扑结构和马达蛋白运动的调控中起着至关重要的作用。然而，这些参数的直接测量在实验上具有挑战性。在这里，我们提出了一种结合角光阱的恒伸长方法，以直接测量 DNA 超螺旋过程中的扭矩。我们在极低的力（约 0.02 pN）下测量了伸展 DNA 的扭转持续长度为 22nm，以及扭结 DNA 的扭转持续长度为 24nm。此外，我们还实施了严格的数据分析方案，将我们的测量结果与现有的 DNA 扭转行为理论模型联系起来。这一套全面的扭转参数表明，对于伸展 DNA 和扭结 DNA，至少有 20%的 DNA 超螺旋被分配到了扭转中。这项工作提供了一种新的实验方法，以及一个分析和解释框架，这将使未来对 DNA 扭转特性的研究得到扩展和增强。
