Niederfrequente Dynamik von überstreckter DNS

对单个DNA分子的微观机械实验表明，将DNA拉伸超过其几何轮廓长度lo所需的力并没有急剧增加，而是达到了一个平台，伸长可达1.7lo。这一平台被解释为正常的BDNA和一种名为S DNA的新结构的共存，在这种结构中，碱基对被认为相对于螺旋轴倾斜。因此，倾斜碱基对之间的Van-der-Waals相互作用的减弱应该会导致DNA的声学性质发生重大变化，这些声学性质直接用非弹性光散射来探测。此外，B-S相变时的构象涨落有望产生丰富的准弹性谱。本项目的目标是使用非弹性和准弹性光散射来详细研究过度拉伸的DNA的动力学和构象波动，这些光散射来自附着在表面力装置板上的定向DNA分子的地毯，或者使用磁场梯度作为力传感器的超顺磁性胶体珠子。这些实验有望揭示力量平台的微观性质，DNA构象波动及其对转录蛋白RecA等蛋白质结合的重要性。

Micromechanical experiments on single DNA molecules have shown that the force required to stretch DNA beyond its geometrical contour length lo does not steeply increase, but reaches a plateau which extends to elongations up to 1.7lo. This plateau has been interpreted as a coexistence between normal B-DNA and a new structure of DNA called S-DNA where the base pairs are thought to be tilted with respect to the helical axis. The reduced van-der-Waals interaction between tilted base pairs should thus entail a significant change in the acoustical properties of the DNA which are directly probed with inelastic light scattering. In addition, the conformational fluctuations at the B-S transition are expected to give rise to a rich quasi-elastic spectrum. The goal of the present project is a detailed study of the dynamics and conformational fluctuations of overstretched DNA using inelastic and quasi-elastic light scattering from carpets of oriented DNA molecules attached to the plates of a surface force apparatus or, alternatively, to super-paramagnetic colloidal beads which are used as force transducers using a magnetic field gradient. These experiments are expected to reveal novel insight into the microscopic nature of the force plateau, into conformational fluctuations in DNA and their importance for the binding of proteins such as the transcription protein RecA.