Ogden S, Haggerty D, Stoner C M, Kolodrubetz D, Schleif R
Proc Natl Acad Sci U S A. 1980 Jun;77(6):3346-50. doi: 10.1073/pnas.77.6.3346.
The locations of DNA binding by the proteins involved with positive and negative regulation of transcription initiation of the L-arabinose operon in Escherichia coli have been determined by the DNase I protection method. Two cyclic AMP receptor protein sites were found, at positions -78 to -107 and -121 to -146, an araC protein--arabinose binding site was found at position -40 to -78, and an araC protein-fucose binding site was found at position -106 to -144. These locations, combined with in vivo data on induction of the two divergently oriented arabinose promoters, suggest the following regulatory mechanism: induction of the araBAD operon occurs when cyclic AMP receptor protein, araC protein, and RNA polymerase are all present and able to bind to DNA. Negative regulation is accomplished by the repressing form of araC protein binding to a site in the regulatory region such that it stimultaneously blocks access of cyclic AMP receptor protein to two sites on the DNA, one site of which serves each of the two promoters. Thus, from a single operator site, the negative regulator represses the two outwardly oriented ara promoters. This regulatory mechanism explains the known positive and negative regulatory properties of the ara promoters.
利用DNA酶I保护法已确定了与大肠杆菌L-阿拉伯糖操纵子转录起始正调控和负调控相关的蛋白质的DNA结合位点。发现了两个环腺苷酸受体蛋白位点，分别位于-78至-107位和-121至-146位，一个阿拉伯糖C蛋白-阿拉伯糖结合位点位于-40至-78位，一个阿拉伯糖C蛋白-岩藻糖结合位点位于-106至-144位。这些位点，再结合关于两个方向相反的阿拉伯糖启动子诱导的体内数据，提示了以下调控机制：当环腺苷酸受体蛋白、阿拉伯糖C蛋白和RNA聚合酶都存在且能够结合到DNA上时，阿拉伯糖BAD操纵子被诱导。负调控是通过阿拉伯糖C蛋白的阻遏形式结合到调控区域的一个位点来实现的，这样它同时阻止环腺苷酸受体蛋白接近DNA上的两个位点，其中一个位点供两个启动子中的每一个使用。因此，从单个操纵基因位点，负调控因子抑制两个向外的阿拉伯糖启动子。这种调控机制解释了阿拉伯糖启动子已知的正调控和负调控特性。
