van Heeswijk W C, Rabenberg M, Westerhoff H V, Kahn D
E. C. Slater Institute, University of Amsterdam, The Netherlands.
Mol Microbiol. 1993 Aug;9(3):443-57. doi: 10.1111/j.1365-2958.1993.tb01706.x.
Regulation of glutamine-synthetase (GS) activity in enteric bacteria involves a complex cascade of events. In response to nitrogen limitation, a transferase catalyses the uridylylation of the PII protein, which in turn stimulates deadenylylation of GS. Deadenylylated GS is the more active form of the enzyme. Here we characterize in detail the genes from Escherichia coli encoding uridylyl-transferase (glnD), the PII protein (glnB), and adenylyl-transferase (glnE). glnD is transcribed from its own promoter, glnE is contranscribed with another gene, orfXE, whereas glnB is partly contranscribed with a gene encoding a homologue of the transcription activator NtrC. All three gln regulatory genes were constitutively expressed at a low level, i.e. their expression was independent of the nitrogen status and the RNA polymerase sigma factor sigma 54. We conclude that the functioning of the GS adenylylation cascade is regulated by modulation of the activities of uridylyl-transferase and adenylyl-transferase, rather than by changes in the expression of their genes.
肠道细菌中谷氨酰胺合成酶（GS）活性的调节涉及一系列复杂的事件。响应氮限制时，一种转移酶催化PII蛋白的尿苷酸化，这反过来又刺激GS的去腺苷酸化。去腺苷酸化的GS是该酶更具活性的形式。在这里，我们详细表征了大肠杆菌中编码尿苷酰转移酶（glnD）、PII蛋白（glnB）和腺苷酰转移酶（glnE）的基因。glnD从其自身的启动子转录，glnE与另一个基因orfXE共转录，而glnB部分与编码转录激活因子NtrC同源物的基因共转录。所有三个谷氨酰胺调节基因均以低水平组成型表达，即它们的表达与氮状态和RNA聚合酶σ因子σ54无关。我们得出结论，GS腺苷酸化级联反应的功能是通过调节尿苷酰转移酶和腺苷酰转移酶的活性来调节的，而不是通过其基因表达的变化来调节的。
