Niederfrequente Dynamik von überstreckter DNS

对单个DNA分子进行的微力学实验表明，拉伸DNA超过其几何轮廓长度lo所需的力不会急剧增加，而是达到一个平台，延伸到1.7lo。这个平台被解释为正常的B-DNA和一种叫做S-DNA的新结构的共存，其中碱基对被认为是相对于螺旋轴倾斜的。因此，倾斜碱基对之间的范德瓦尔斯相互作用的减少应该导致DNA声学特性的显著变化，这是用非弹性光散射直接探测的。此外，B-S跃迁的构象波动预计会产生丰富的准弹性谱。本项目的目标是详细研究过度拉伸DNA的动力学和构象波动，使用非弹性和准弹性光散射，这些光散射来自附着在表面力装置板上的定向DNA分子地毯，或者用于使用磁场梯度作为力传感器的超顺磁性胶体珠。这些实验有望揭示力平台的微观性质，DNA构象波动及其对转录蛋白RecA等蛋白质结合的重要性的新见解。

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.