Straney S B, Crothers D M
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06511.
Cell. 1987 Dec 4;51(5):699-707. doi: 10.1016/0092-8674(87)90093-6.
We show, using a combination of methods, that contrary to the usual view, lac repressor increases, by more than 100-fold, the initial binding of RNA polymerase to E. coli lac UV5 promoter DNA. Kinetic studies revealed that the repressor acts to block the isomerization step in transcription initiation. When IPTG, a gratuitous inducer, is added, formation of open complex and productive transcription proceed. Because of the large increases in the binding constant, at low polymerase concentrations the presence of lac repressor (and then inducer) actually increases the rate of the first round of productive transcription, thus allowing the system to respond rapidly to the release of repression. This dual role of stabilization of a pretranscriptional complex coupled with blockage of transcription initiation may be a more general model for genetic regulation than that provided by the concept of simple repression.
我们使用多种方法表明，与通常观点相反，乳糖阻遏物使RNA聚合酶与大肠杆菌乳糖UV5启动子DNA的初始结合增加了100多倍。动力学研究表明，阻遏物的作用是阻断转录起始中的异构化步骤。当加入异丙基-β-D-硫代半乳糖苷（IPTG，一种安慰诱导剂）时，开放复合物的形成和有效转录得以进行。由于结合常数大幅增加，在低聚合酶浓度下，乳糖阻遏物（以及随后的诱导剂）的存在实际上提高了第一轮有效转录的速率，从而使系统能够对阻遏的解除迅速做出反应。这种转录前复合物稳定与转录起始阻断的双重作用，可能是一种比简单阻遏概念更普遍的基因调控模型。
