Meyer-Almes F J, Heumann H, Porschke D
Max Planck Institut für biophysikalische Chemie, Göttingen, Germany.
J Mol Biol. 1994 Feb 11;236(1):1-6. doi: 10.1006/jmbi.1994.1112.
The complex formed between RNA polymerase holoenzyme from Escherichia coli and the strong promoter A1 from the phage T7 has been characterized by measurements of the electric dichroism. The dichroism decay time constant of a promoter DNA fragment with 126 bp increases upon binding of the polymerase, but the increase is less than expected for simple addition of the components at the known binding site. Our results demonstrate a protein-induced decrease of the hydrodynamic DNA dimensions, which is not a consistent with an increased flexibility, but indicates bending of the double helix with a relatively narrow distribution of bending angles. We have characterized the degree of DNA bending by bead model simulations and used, in addition to our present experimental data, the available information on the overall size and shape of the RNA polymerase, together with the location of the DNA bending center at the starting point of RNA synthesis. We conclude that the bending angle is 45 degrees (+/- 5 degrees).
通过测量电二色性对大肠杆菌RNA聚合酶全酶与噬菌体T7的强启动子A1形成的复合物进行了表征。随着聚合酶的结合，126 bp启动子DNA片段的二色性衰减时间常数增加，但增加幅度小于在已知结合位点简单添加各组分时的预期值。我们的结果表明蛋白质诱导了流体动力学DNA尺寸的减小，这与柔韧性增加不一致，而是表明双螺旋发生弯曲，且弯曲角度分布相对较窄。我们通过珠子模型模拟表征了DNA弯曲程度，除了当前的实验数据外，还利用了关于RNA聚合酶整体大小和形状的现有信息，以及DNA弯曲中心在RNA合成起始点的位置。我们得出结论，弯曲角度为45度（±5度）。
