Ghrist A C, Stauffer G V
Department of Microbiology, University of Iowa, Iowa City 52242, USA.
J Bacteriol. 1995 Sep;177(17):4980-4. doi: 10.1128/jb.177.17.4980-4984.1995.
The Escherichia coli glycine cleavage enzyme system catalyzes the cleavage of glycine, generating CO2, NH3, and a one-carbon unit. Expression of the operon encoding this enzyme system (gcv) is induced in the presence of glycine and repressed in the presence of purines. In this study, a mutant with high-level constitutive expression of a gcvT-lacZ gene fusion was isolated. The mutation in this strain was designated gcvR1 and was mapped to min 53.3 on the E. coli chromosome. A single-copy plasmid carrying the wild-type gcvR gene complemented the mutation, restoring normal regulation of a gcvT-lacZ fusion, while a multicopy plasmid carrying gcvR led to superrepression under all growth conditions. Negative regulation of a gcvT-lacZ fusion by GcvR was shown to require GcvA, a LysR family protein known to both activate gcv in the presence of glycine and repress gcv in the presence of purines. Models explaining how GcvR and GcvA might interact to regulate gcv expression are proposed.
大肠杆菌甘氨酸裂解酶系统催化甘氨酸的裂解,生成二氧化碳、氨和一个一碳单位。编码该酶系统(gcv)的操纵子在甘氨酸存在时被诱导表达,在嘌呤存在时被抑制表达。在本研究中,分离出了一个gcvT-lacZ基因融合体高水平组成型表达的突变体。该菌株中的突变被命名为gcvR1,定位于大肠杆菌染色体上的53.3分钟处。携带野生型gcvR基因的单拷贝质粒可互补该突变,恢复gcvT-lacZ融合体的正常调控,而携带gcvR的多拷贝质粒在所有生长条件下均导致超抑制。结果表明,GcvR对gcvT-lacZ融合体的负调控需要GcvA,GcvA是一种赖氨酸R家族蛋白,已知在甘氨酸存在时激活gcv,在嘌呤存在时抑制gcv。本文提出了解释GcvR和GcvA如何相互作用以调控gcv表达的模型。