论文部分内容阅读
促旋酶(gyrase)在原核生物的生命活动中扮演着重要的角色,它是已知拓扑异构酶中,唯一能够向DNA引入负超螺旋的酶.本文中,我们利用磁镊(magnetic tweezers)对促旋酶和DNA的相互作用进行了单分子实时观测.实验发现,在不加入ATP时,促旋酶能够同时与两段DNA(G片段和T片段)结合,但这种结合较弱,施加0.7pN的外力就能逐渐破坏两者的结合;但加入高浓度的诺氟沙星后,促旋酶与DNA的结合明显增强,甚至能够抗衡5.9pN的外力.促旋酶还会影响超螺旋的几何尺度:不加入促旋酶时,DNA超螺旋的几何尺度由DNA所受拉力决定,而加入促旋酶后,超螺旋DNA几何尺度变小,并且主要由DNA与促旋酶的相互作用而不再是所受拉力所决定.而且促旋酶与正负超螺旋的结合能力不同,它更容易与正超螺旋结合.同时,发现促旋酶从DNA上解离的时间符合双指数分布.我们提出的模型能够很好地解释这个分布,并与他人提出的模型的结果进行了比较.
Gyrase plays an important role in the life activity of prokaryotes, and it is the only one of the known topoisomerases that can introduce negative supercoiled DNA into the DNA.In this paper, we use magnetic tweezers ), A single molecule real-time observation of the interaction between gyrase and DNA was carried out.It was found that gyrase could bind to two DNA fragments (G fragment and T fragment) at the same time without adding ATP, but the binding was weak , Exert 0.7pN external force can gradually undermine the combination of the two; However, the addition of high concentrations of norfloxacin, gyrase and DNA binding significantly enhanced, and even able to contend the external force of 5.9pN. Gyrase also affect The geometric scale of supercoils: When gyrase is not added, the geometric dimension of DNA supercoils is determined by the pulling force of DNA. After addition of gyrase, the geometric dimensions of supercoiled DNA become smaller, and mainly due to the interaction between DNA and gyrase Interaction is no longer determined by the pulling force.Moreover, gyrase has different binding ability with positive and negative supercoils, it is easier to combine with positive supercoils.Meanwhile, it was found that the time for gyrase to dissociate from DNA was in accordance with the double Exponential distribution. The model we proposed can explain this distribution very well, The results of the model with others proposed were compared.