Strick T R, Allemand J F, Bensimon D, Croquette V
Laboratoire de Physique Statistique de l'ENS, URA 1306 CNRS, Associé aux Universités Paris VI et VII, France.
Biophys J. 1998 Apr;74(4):2016-28. doi: 10.1016/S0006-3495(98)77908-1.
We study DNA supercoiling in a quantitative fashion by micromanipulating single linear DNA molecules with a magnetic field gradient. By anchoring one end of the DNA to multiple sites on a magnetic bead and the other end to multiple sites on a glass surface, we were able to exert torsional control on the DNA. A rotating magnetic field was used to induce rotation of the magnetic bead, and reversibly over- and underwind the molecule. The magnetic field was also used to increase or decrease the stretching force exerted by the magnetic bead on the DNA. The molecule's degree of supercoiling could therefore be quantitatively controlled and monitored, and tethered-particle motion analysis allowed us to measure the stretching force acting on the DNA. Experimental results indicate that this is a very powerful technique for measuring forces at the picoscale. We studied the effect of stretching forces ranging from 0.01 pN to 100 pN on supercoiled DNA (-0.1 < sigma < 0.2) in a variety of ionic conditions. Other effects, such as stretching-relaxing hysteresis and the braiding of two DNA molecules, are discussed.
我们通过利用磁场梯度对单个线性DNA分子进行微操作，以定量方式研究DNA超螺旋。通过将DNA的一端固定在磁珠上的多个位点，另一端固定在玻璃表面的多个位点，我们能够对DNA施加扭转控制。使用旋转磁场诱导磁珠旋转，并使分子可逆地过度缠绕和欠缠绕。磁场还用于增加或减少磁珠对DNA施加的拉伸力。因此，可以定量控制和监测分子的超螺旋程度，并且系链粒子运动分析使我们能够测量作用在DNA上的拉伸力。实验结果表明，这是一种在皮牛尺度上测量力的非常强大的技术。我们研究了在各种离子条件下，从0.01皮牛到100皮牛的拉伸力对超螺旋DNA（-0.1 < σ < 0.2）的影响。还讨论了其他效应，如拉伸-松弛滞后和两个DNA分子的编织。
