| FlhD and FlhC proteins are currently characterized as global regulators. Initially, FlhD/FlhC protein complex was described as the master regulator of genes involved in the synthesis of flagella and the chemotaxis system. However, recent studies have found that the FlhDC complex and FIND without FlhC function in the regulation of many more genes.; As cells are entering stationary phase, FlhDC functions in negatively regulating acid stress response genes. One acid stress gene that encodes a glutamate decarboxylase enzyme is the gadA gene. FlhDC negatively regulates gadA and binds to the promoter. The binding to the gadA promoter is mediated through the helix-turn-helix DNA binding motif on the FlhC molecule. However, the helix-turn-helix motif has no affect on the binding to the flhB promoter DNA, which encodes a flagella transport apparatus.; Additionally, upon FlhDC binding, the complex bends the flhB promoter DNA at 111° versus the gadA promoter DNA that does not bend at all. FlhDC affinity for the gadA promoter is significantly less than to the flhB promoter. In addition, the FlhDC requires the presence of Gad regulators, GadX/GadW to repress gadA.; FlhDC seems to bind the gadA promoter in a linear fashion across the helix-turn-helix motif of the FlhC monomers. The binding of the flagella promoter, flhB, and non-flagella promoter. gadA, requires different regions within the FlhDC molecule. In addition, the GadXW regulators may enhance the FlhDC binding to the gadA promoter. |
