Reitzer L J, Magasanik B
Proc Natl Acad Sci U S A. 1985 Apr;82(7):1979-83. doi: 10.1073/pnas.82.7.1979.
We have determined that the glnA gene of the complex glnALG operon of Escherichia coli is transcribed from tandem promoters. Expression from the upstream promoter, glnAp1, requires the catabolite activating protein, is repressed by nitrogen regulator I (NRI), the product of glnG, and produces a transcript with an untranslated leader of 187 nucleotides. Expression from the downstream promoter, glnAp2, requires NRI as well as the glnF product; full expression also requires growth in a nitrogen-limited environment. The downstream transcript has an untranslated leader of 73 nucleotides. We also provide evidence that the function of the glnL product is to mediate the interconversion of NRI between a form capable of activating glnAp2 and an inactive form in response to changes in the intracellular concentration of ammonia. The function of the two minor promoters of the glnALG operon, glnAp1 and glnLp, is to maintain the products of glnA, glutamine synthetase, an essential enzyme, and of glnG, NRI, an activator of nitrogen-controlled genes, during carbon-limited growth.
我们已经确定，大肠杆菌复杂的glnALG操纵子的glnA基因由串联启动子转录。上游启动子glnAp1的表达需要分解代谢物激活蛋白，受氮调节因子I（NRI，glnG的产物）抑制，并产生一个具有187个核苷酸非翻译前导序列的转录本。下游启动子glnAp2的表达需要NRI以及glnF产物；完全表达还需要在氮限制环境中生长。下游转录本有一个73个核苷酸的非翻译前导序列。我们还提供证据表明，glnL产物的功能是介导NRI在能够激活glnAp2的形式和响应细胞内氨浓度变化的无活性形式之间的相互转化。glnALG操纵子的两个次要启动子glnAp1和glnLp的功能是在碳限制生长期间维持glnA（谷氨酰胺合成酶，一种必需酶）和glnG（NRI，氮控制基因的激活剂）的产物。
