Lefèvre J F, Lane A N, Jardetzky O
Stanford Magnetic Resonance Laboratory, Stanford University, California 94305.
Biochemistry. 1988 Feb 23;27(4):1086-94. doi: 10.1021/bi00404a002.
Selective changes in the NMR parameters of the sequence of CGTACTAGTTAACTAGTACG, which corresponds to the trp operator of Escherichia coli, were observed as a function of temperature. The changes were localized to the sequence TTAA in the Pribnow box (underlined). Differential changes in chemical shift were analyzed in terms of a three-state model (states I, II, and III) to give the equilibrium constants, enthalpy changes, and populations. The midpoints of the first and second transitions were 9 and 30 degrees C, with enthalpy changes of 58 and 35 kcal/mol, respectively. Measurement of the spin-lattice and cross-relaxation rate constants at different temperatures allowed some structural conclusions to be drawn about the nature of the transitions. The line width of the H2 of A11 goes through a maximum at about 30 degrees C, indicating moderately fast exchange between the states. The rate constants for exchange at the midpoints were about 200 (I----II) and 250 (II----III) s-1. Taking these findings into account, we propose a mechanism for the interaction between RNA polymerase and the promoter. This mechanism can explain the temperature dependence observed for the initiation of transcription.
观察到与大肠杆菌色氨酸操纵基因相对应的CGTACTAGTTAACTAGTACG序列的核磁共振参数随温度发生选择性变化。这些变化局限于Pribnow框中的TTAA序列（下划线部分）。根据三态模型（状态I、II和III）分析化学位移的差异变化，以得出平衡常数、焓变和丰度。第一次和第二次转变的中点分别为9℃和30℃，焓变分别为58千卡/摩尔和35千卡/摩尔。在不同温度下测量自旋晶格和交叉弛豫速率常数，从而可以得出一些关于转变性质的结构结论。A11的H2的线宽在约30℃时达到最大值，表明状态之间的交换速度适中。中点处的交换速率常数约为200（I→II）和250（II→III）秒-1。考虑到这些发现，我们提出了一种RNA聚合酶与启动子之间相互作用的机制。该机制可以解释观察到的转录起始的温度依赖性。
