Heil Gary, Stauffer Lorraine T, Stauffer George V
Department of Microbiology, The University of Iowa, Iowa City, IA 52242, USA1.
Microbiology (Reading). 2002 Jul;148(Pt 7):2203-2214. doi: 10.1099/00221287-148-7-2203.
The Escherichia coli gcvTHP operon is under control of the LysR-type transcriptional regulator GcvA. GcvA activates the operon in the presence of glycine and represses the operon in its absence. Repression by GcvA is dependent on a second regulatory protein, GcvR. Generally, LysR-type transcriptional regulators bind to specific small co-effector molecules which results in either their altered affinity for specific binding sites on the DNA or altered ability to bend the DNA, resulting in either activation or repression of their respective operons. This study shows that glycine, the co-activator for the gcv operon, does not alter either GcvA's ability to bind DNA nor its ability to bend DNA. Rather, glycine binds to GcvR, disrupting a GcvA/GcvR interaction required for repression and allowing GcvA activation of the gcvTHP operon. Amino acid changes in GcvR that reduce glycine binding result in a loss of glycine-mediated activation in vivo.
大肠杆菌的gcvTHP操纵子受LysR型转录调节因子GcvA的调控。在有甘氨酸存在的情况下，GcvA激活该操纵子，而在没有甘氨酸时则抑制该操纵子。GcvA的抑制作用依赖于另一种调节蛋白GcvR。一般来说，LysR型转录调节因子与特定的小分子辅效应物分子结合，这会导致它们对DNA上特定结合位点的亲和力改变，或者改变其弯曲DNA的能力，从而导致各自操纵子的激活或抑制。这项研究表明，作为gcv操纵子共激活剂的甘氨酸，既不会改变GcvA与DNA结合的能力，也不会改变其弯曲DNA的能力。相反，甘氨酸与GcvR结合，破坏了抑制所需的GcvA/GcvR相互作用，并使GcvA激活gcvTHP操纵子。GcvR中减少甘氨酸结合的氨基酸变化导致体内甘氨酸介导的激活作用丧失。
