Redox signal transduction by the ArcB sensor kinase of Haemophilus influenzae lacking the PAS domain

The Arc (anoxic redox control) two-component signal transduction system of Escherichia coli, which comprises the tripartite ArcB sensor kinase and the ArcA response regulator, modulates the expression of numerous operons in r esponse to redox conditions of growth. We demonstrate that the arcA and arc B genes of Haemophilus influenzae specify a two-component system. The Arc p roteins of the two bacterial species sufficiently resemble each other that they can participate in heterologous transphosphorylation in vitro. Moreove r, the Arc system of H. influenzae mediates transcriptional control accordi ng to the redox condition of growth both autologously in its own host and h omologously in E. coli, indicating a high degree of functional conservation of the signal transduction system. The H. influenzae ArcB, however, lacks the PAS domain present in the region of E. coli ArcB; linking the transmemb rane to the cytosolic catalytic domains. Because the PAS domain participate s in signal reception in a variety of sensory proteins, including sensors o f molecular oxygen and redox state, a similar role was previously ascribed to it in ArcB. Our results demonstrate that the ArcB protein of H. influenz ae mediates signal transduction in response to redox conditions of growth d espite the absence of the PAS domain.