Identification of UvrY as the cognate response regulator for the BarA sensor kinase in Escherichia coli.

BarA is a membrane-associated protein that belongs to a subclass of tripartite sensors of the two-component signal transduction system family. In this study, we report that UvrY is the cognate response regulator for BarA of Escherichia coli. This conclusion is based upon homologies with analogous two-component systems and demonstrated by both biochemical and genetic means. We show that the purified BarA protein is able to autophosphorylate when incubated with [gamma-(32)P]ATP but not with [alpha-(32)P]ATP or [gamma-(32)P]GTP. Phosphorylated BarA, in turn, acts as an efficient phosphoryl group donor to UvrY but not to the non-cognate response regulators ArcA, PhoB, or CpxR. The specificity of the transphosphorylation reaction is further supported by the fact that UvrY can receive the phosphoryl group from BarA-P but not from the non-cognate tripartite sensor ArcB-P or ATP. In addition, genetic evidence that BarA and UvrY mediate the same signal transduction pathway is provided by the finding that both uvrY and barA mutant strains exhibit the same hydrogen peroxide hypersensitive phenotype. These results provide the first biochemical evidence as well as genetic support for a link between BarA and UvrY, suggesting that the two proteins constitute a new two-component system for gene regulation in Escherichia coli.