Interpretation of monovalent and divalent cation effects on the lac repressor-operator interaction.
Interpretation of monovalent and divalent cation effects on the lac repressor-operator interaction.
复制标题
单价和二价阳离子对 lac 阻遏物-操纵子相互作用的影响的解释。
作者：
M. Record;P. Dehaseth;T. Lohman
我们研究了混合 Na+: Mg2+ 离子溶液对非特异性紫胶阻遏物-DNA 复合物稳定性的影响。 Mg2+ 的作用可以简单地解释为其作为 DNA 位点竞争者（具有阻遏物）的作用。从这些研究中，可以确定 Mg-DNA 复合物的结合常数与 Na+ 浓度的函数关系。我们使用这些信息来解释 Riggs 和合作者 (Riggs, A.D., et al. (1970), J. Mol. Biol. 48, 67-83; 53, 401-417) 关于阻遏蛋白-操纵子相互作用的离子依赖性的数据。我们发现阻遏蛋白-操纵子复合物中的离子相互作用大约是非特异性复合物中的 70%。我们的最佳估计是形成 8 +/- 1 个离子对。我们计算出，在体内离子条件下缔合反应中，特定复合物形成过程中抗衡离子的释放贡献了约 40% 的有利自由能变化。考虑了这些发现对 lac 操纵子的控制以及特异性和非特异性复合物之间的分子关系的影响。
We have investigated the effects of mixed Na+: Mg2+ ionic solutions on the stability of the nonspecific lac repressor-DNA complex. The effects of Mg2+ are simply interpreted in terms of its role as a competitor (with repressor) for DNA sites. From these studies, the binding constant of the Mg-DNA complex can be determined as a function of the concentration of Na+. We have used this information to interpret the data of Riggs and collaborators (Riggs, A.D., et al. (1970), J. Mol. Biol. 48, 67-83; 53, 401-417) on the ion dependence of the repressor-operator interaction. We find that there are approximately 70% as many ionic interactions in the repressor-operator complex as in the nonspecific complex. Our best estimate is that 8 +/- 1 ion pairs are formed. We calculate that the release of counterions in the formation of the specific complex contributes approximately 40% of the favorable free energy change in the association reaction under in vivo ionic conditions. Implications of these findings for the control of the lac operon and for the molecular relationship between the specific and nonspecific complexes are considered.