ArgP is a LysR-type transcriptional regulator (LTTR) that operates with two effector molecules, lysine and arginine, to differentially regulate gene expression. Effector-free ArgP stimulates transcription of all investigated regulon members, except argO, whereas lysine abolishes this effect. Activation of argO, encoding an exporter for arginine and canavanine, is strictly dependent on arginine-bound ArgP. Lysine counteracts this effect and even though lysine-bound ArgP stimulates RNA polymerase recruitment at the argO promoter, the complex is non-productive. It is presently unclear what distinguishes argO from other ArgP targets and how binding of arginine and lysine translates in antagonistic effects on promoter activity. Here we generate high resolution contact maps of effector-free and effector-bound ArgP-DNA interactions and identify the sequence 5′-CTTAT as the consensus recognition motif for ArgP binding. argO is the only operator at which ArgP binding overlaps the −35 promoter element and binding of arginine results in a repositioning of the promoter proximal bound ArgP-arg subunits. This effect was mimicked by the generation of a 10 bp insertion mutant (ins-10) in the argO operator that renders its activation by ArgP arginine-independent. ArgP-induced DNA bending of the argO operator by approximately 60° was found to be effector independent. An ArgP:DNA binding stoichiometry of 4:1 indicates binding of four ArgP subunits even to DNA constructs that are truncated for one binding subsite (ΔABS). These results provide insight into the molecular mechanisms of ArgP-mediated regulation and a molecular explanation for the unique arginine-dependence of argO activation that distinguishes this particular ArgP target from all others.

ArgP是一种LysR型转录调节因子（LTTR），可与两个效应分子赖氨酸和精氨酸一起起作用，以差异地调节基因表达。不含效应子的ArgP刺激除argO之外的所有研究过的调节子成员的转录，而赖氨酸则消除了这种效应。argO的激活严格编码与精氨酸结合的ArgP，该argO编码精氨酸和canavanine的输出蛋白。赖氨酸抵消了这种作用，即使赖氨酸结合的ArgP刺激了argO启动子处的RNA聚合酶募集，该复合物也没有产生作用。目前尚不清楚argO有何区别精氨酸和赖氨酸的结合如何转化为对启动子活性的拮抗作用。在这里，我们生成无效应子和效应子结合的ArgP-DNA相互作用的高分辨率接触图，并将序列5'-CTTAT识别为ArgP结合的共有识别基序。argO是ArgP结合与-35启动子元件重叠的唯一操纵子，精氨酸的结合导致启动子近端结合的ArgP-arg亚基重新定位。可以通过在argO操纵子中产生10 bp的插入突变体（ins-10）来模仿此效果，该突变体可通过ArgP精氨酸独立性激活它。ArgP诱导的DNA弯曲的ARGO发现大约60°的操作者是独立于效应子的。ArgP：DNA结合化学计量比为4：1表示四个ArgP亚基甚至与被截短一个结合亚位点（ΔABS）的DNA构建体结合。这些结果提供了对ArgP介导的调节的分子机制的深入了解，并为argO活化的独特精氨酸依赖性提供了分子解释，该依赖性使该特定ArgP靶标与其他靶标区别开来。