THE TWIST, WRITHE AND OVERALL SHAPE OF SUPERCOILED DNA CHANGE DURING COUNTERION-INDUCED TRANSITION FROM A LOOSELY TO A TIGHTLY INTERWOUND SUPERHELIX - POSSIBLE IMPLICATIONS FOR DNA-STRUCTURE IN-VIVO
THE TWIST, WRITHE AND OVERALL SHAPE OF SUPERCOILED DNA CHANGE DURING COUNTERION-INDUCED TRANSITION FROM A LOOSELY TO A TIGHTLY INTERWOUND SUPERHELIX - POSSIBLE IMPLICATIONS FOR DNA-STRUCTURE IN-VIVO
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DOI：
10.1006/jmbi.1994.1042
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发表时间：
1994-01-21
影响因子：
5.6
通讯作者：
BATES, AD
中科院分区：
文献类型：
--
作者：
BEDNAR, J;FURRER, P;BATES, AD
超螺旋DNA分子自由悬浮在冷冻玻璃化缓冲液的冷冻电子显微镜研究相结合的Monte Carlo模拟和凝胶电泳分析，以调查的作用，决定超螺旋DNA分子的形状的片段间的静电排斥。它在这里表明，通过增加浓度的抗衡离子的DNA-DNA排斥的减少导致更高的分数的连接数赤字被分配到扭动。当抗衡离子达到可能存在于体内条件下的浓度时，天然超螺旋质粒采用紧密缠绕的构象。在这些紧密超螺旋的DNA分子中，相互缠绕的超螺旋的相对片段似乎直接彼此接触。在超螺旋微环（178 bp）的特殊情况下，ΔLk= -2拓扑异构体经历了一个急剧的结构转变，从低盐缓冲液中几乎是平面的圆形转变为含有中和浓度的反离子的缓冲液中强烈扭曲的“8”字形构象。这种观察到的DNA结构转变的可能影响进行了讨论。
A cryo-electron microscopy study of supercoiled DNA molecules freely suspended in cryo-vitrified buffer was combined with Monte Carlo simulations and gel electrophoretic analysis to investigate the role of intersegmental electrostatic repulsion in determining the shape of supercoiled DNA molecules. It is demonstrated here that a decrease of DNA-DNA repulsion by increasing concentrations of counterions causes a higher fraction of the linking number deficit to be partitioned into writhe. When counterions reach concentrations likely to be present underin vivoconditions, naturally supercoiled plasmids adopt a tightly interwound conformation. In these tightly supercoiled DNA molecules the opposing segments of interwound superhelix seem to directly contact each other. This form of supercoiling, where two DNA helices interact laterally, may represent an important functional state of DNA.In the particular case of supercoiled minicircles (178 bp) the ΔLk= -2 topoisomers undergo a sharp structural transition from almost planar circles in low salt buffers to strongly writhed "figure-eight" conformations in buffers containing neutralizing concentrations of counterions. Possible implications of this observed structural transition in DNA are discussed.