Hammermann M, Steinmaier C, Merlitz H, Kapp U, Waldeck W, Chirico G, Langowski J
Division of Biophysics of Macromolecules, German Cancer Research Center, Heidelberg.
Biophys J. 1997 Nov;73(5):2674-87. doi: 10.1016/S0006-3495(97)78296-1.
Using laser light scattering, we have measured the static and dynamic structure factor of two different superhelical DNAs, p1868 (1868 bp) and simian virus 40 (SV40) (5243 bp), in dilute aqueous solution at salt concentrations between 1 mM and 3 M NaCl. For both DNA molecules, Brownian dynamics (BD) simulations were also performed, using a previously described model. A Fourier mode decomposition procedure was used to compute theoretical light scattering autocorrelation functions (ACFs) from the BD trajectories. Both measured and computed autocorrelation functions were then subjected to the same multiexponential decomposition procedure. Simulated and measured relaxation times as a function of scattering angle were in very good agreement. Similarly, computed and measured static structure factors and radii of gyration agreed within experimental error. One main result of this study is that the amplitudes of the fast-relaxing component in the ACF show a peak at 1 M salt concentration. This nonmonotonic behavior might be caused by an initial increase in the amplitudes of internal motions due to diminishing long-range electrostatic repulsions, followed by a decrease at higher salt concentration due to a compaction of the structure.
利用激光光散射技术，我们测量了两种不同超螺旋DNA（p1868，1868碱基对；猿猴病毒40，SV40，5243碱基对）在1 mM至3 M NaCl盐浓度范围内的稀水溶液中的静态和动态结构因子。对于这两种DNA分子，还使用先前描述的模型进行了布朗动力学（BD）模拟。采用傅里叶模式分解程序从BD轨迹计算理论光散射自相关函数（ACF）。然后，对测量和计算得到的自相关函数都进行相同的多指数分解程序。模拟和测量得到的弛豫时间作为散射角的函数，两者吻合得非常好。同样，计算和测量得到的静态结构因子和回转半径在实验误差范围内相符。这项研究的一个主要结果是，ACF中快速弛豫成分的振幅在1 M盐浓度处出现一个峰值。这种非单调行为可能是由于远程静电排斥力减弱导致内部运动振幅最初增加，随后在较高盐浓度下由于结构压缩而减小所致。
