Ellison M J, Fenton M J, Ho P S, Rich A
EMBO J. 1987 May;6(5):1513-22. doi: 10.1002/j.1460-2075.1987.tb02394.x.
Local DNA conformations that are underwound with respect to the right-handed B form are favored in negatively supercoiled DNA. However, when multiple transitional events co-exist within a common topological domain, they must compete with one another for the available free energy of negative supercoiling. Recently we developed a general theoretical model capable of predicting the behavior at equilibrium of defined sequences in a variety of competitive situations. In the present work we have applied this theory to predict the formation of Z-DNA as a function of superhelicity in stretches of d(CG)m and d(CA)n when they are forced to compete with one another in the same plasmid. The observed behavior of these competing sequences is in close accord with theoretical predictions. These results indicate that sequences separated by large distances can effect the transitional behavior of each other in a complex manner which is independent of the relative orientation of the participating segments. The pattern of transitional events is strongly dependent on levels of DNA supercoiling, ambient conditions and on the nature and number of the sequences involved. Although in the present work we apply the model specifically to the Z-DNA conformational transition, the results of this study may have general relevance to a variety of biological processes in which the helical repeat of DNA is reversibly altered, including the initial steps in transcription, replication and recombination.
相对于右手B型而言处于欠旋状态的局部DNA构象在负超螺旋DNA中更受青睐。然而，当多个转变事件在一个共同的拓扑结构域中共存时，它们必须相互竞争负超螺旋的可用自由能。最近我们开发了一个通用理论模型，能够预测在各种竞争情况下特定序列在平衡状态下的行为。在本研究中，我们应用该理论来预测在同一质粒中d(CG)m和d(CA)n片段中Z-DNA的形成与超螺旋度的函数关系，此时它们被迫相互竞争。这些竞争序列的观察行为与理论预测非常吻合。这些结果表明，相隔很远的序列能够以一种复杂的方式影响彼此的转变行为，这种方式与参与片段的相对取向无关。转变事件的模式强烈依赖于DNA超螺旋水平、环境条件以及所涉及序列的性质和数量。虽然在本研究中我们将该模型专门应用于Z-DNA构象转变，但本研究结果可能与DNA螺旋重复被可逆改变的各种生物过程普遍相关，包括转录、复制和重组的起始步骤。
