Figure 1.

Two-component signal transduction in pathogenesis. Signals (external stimuli) residing in the host environment are recognized by the bacterium and stimulate the histidine protein kinase(s) to autophosphorylate (shown in the schematic as the bracketed HPK-P). Each phosphorylated histidine protein kinase (HPK) is mated to a specific response regulator (RR) to which it initiates phosphoryl transfer. Phosphorylation of the response regulator (RR-P) relieves inhibition of its transcriptional activation properties resulting in transcription and expression of the genes that it controls.