Equilibrium binding of inducer to lac repressor.operator DNA complex.
Equilibrium binding of inducer to lac repressor.operator DNA complex.
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DOI：
10.1016/s0021-9258(19)70434-7
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发表时间：
1980-11
期刊：
影响因子：
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通讯作者：
R. B. O'Gorman;J. Rosenberg;O. B. Kallai;R. Dickerson;K. Itakura;A. Riggs;K. Matthews
中科院分区：
文献类型：
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作者：
R. B. O'Gorman;J. Rosenberg;O. B. Kallai;R. Dickerson;K. Itakura;A. Riggs;K. Matthews
研究了在存在一个小的(29个碱基对)操纵子DNA片段时，诱导剂与乳糖抑制蛋白结合的特征。操纵子DNA片段的存在降低了蛋白质对诱导剂分子的亲和力。观察到的最大变化是蛋白质半饱和所需的诱导剂浓度增加了20倍。结合数据的Scatchard类型图和Hill图的斜率的非线性表明，在操纵子DNA片段存在的情况下，诱导剂结合表现出协同行为，而自由抑制物以非合作的方式结合诱导剂。在存在和不存在饱和量的操纵子DNA片段的情况下，诱导剂与抑制物结合的实验数据与几个不同模型预测的曲线进行了比较。使用阻遏物-操纵子DNA-诱导物相互作用的测量值设置的限制，可以区分不同的模型。准确预测诱导物结合曲线并与其他参数实测值吻合较好的模型为Monod-Wyman-Changeux和Koshland模型，具有以下特点：1)诱导物与阻遏物结合的正协同性。操纵子DNA复合体；2)操纵子DNA片段与阻遏蛋白结合的两个位点；3)每个操纵子DNA片段与阻遏蛋白全部四个亚基结合的效果。这些模型与所有可用的数据是一致的，它们表明前两个诱导剂分子的结合占自由和诱导阻遏物与操纵子DNA亲和力差异的60%以上；在体内，这种差异应该足以诱导发生。
The characteristics of inducer binding to lactose repressor protein in the presence of a small (29 base pair) operator DNA fragment have been examined. The presence of operator DNA fragments decreases the affinity of the protein for inducer molecules. The maximum change observed is a 20-fold increase in the concentration of inducer necessary for half-saturation of the protein. The non-linearity of the Scatchard type plots and slopes of the Hill plots of the binding data indicate that inducer binding exhibits cooperative behavior in the presence of operator DNA fragments, while free repressor binds inducer in a noncooperative fashion. The experimental data for the binding of inducer to repressor both in the presence and absence of saturating amounts of operator DNA fragments were compared to curves predicted by several different models. Using the limits placed by the measured values for repressor-operator DNA-inducer interaction, it was possible to discriminate between the various models. The models which accurately predicted the inducer binding curves and conformed to the measured values for the other parameters were Monod-Wyman-Changeux and Koshland type models with the following features: 1) positive cooperativity in the binding of inducer to the repressor . operator DNA complex; 2) two sites for the binding of the operator DNA fragment to repressor protein; 3) effect of binding of each operator DNA fragment on all four subunits of the repressor. These models are consistent with all of the available data, and they indicate that the binding of the first two inducer molecules accounts for greater than or equal to 60% of the difference in affinities between free and induced repressor for operator DNA; in vivo this difference should be sufficient for induction to occur.