Williams J, Michan C, Webster C, Busby S
School of Biochemistry, University of Birmingham, U.K.
Biochem J. 1994 Jun 15;300 ( Pt 3)(Pt 3):757-63. doi: 10.1042/bj3000757.
The Escherichia coli MelR protein binds to two sites at the melAB promoter and activates transcription in response to melibiose. The binding of purified MelR to the melAB promoter and to a number of derivatives carrying point mutations has been studied. A melAB promoter fragment that is very weakly activated by the melR gene product has been made by creating multiple symmetrical changes in both MelR-binding sites. A library of random substitutions in MelR was screened to find mutants that were able to activate this mutant promoter. One of these mutants contained a substitution in a proposed helix-turn-helix region that most likely relaxes the sequence-specificity of MelR binding. The other mutants contain substitutions throughout the central part of MelR and appear to alter the conformation of MelR, such that activity is triggered at lower melibiose concentrations and by arabinose.
大肠杆菌MelR蛋白与melAB启动子的两个位点结合，并响应蜜二糖激活转录。已经研究了纯化的MelR与melAB启动子以及携带点突变的多种衍生物的结合情况。通过在两个MelR结合位点产生多个对称变化，构建了一个被melR基因产物激活程度非常弱的melAB启动子片段。对MelR中随机取代的文库进行筛选，以找到能够激活这个突变启动子的突变体。其中一个突变体在一个推测的螺旋-转角-螺旋区域发生了取代，这很可能放松了MelR结合的序列特异性。其他突变体在MelR的中部各处都有取代，似乎改变了MelR的构象，从而使得在较低的蜜二糖浓度下以及被阿拉伯糖触发活性。
