The BarA-UvrY two-component signal transduction system has been described in several animal and plant pathogens, such as Escherichia, Pseudomonas, Vibrio, Erwinia, Legionella, and Salmonella genera, and has been associated with phenotypes such as motility, biofilm formation and pathogenic interactions. The target genes are not well defined, although there is a strong connection to virulence functions as the expression of numerous virulence genes, specific to each pathogen, are controlled by this system. We propose to probe for the physiological signals that stimulate the BarA sensor kinase, to elucidate the routes of phosphoryl-group transfer for signal transmission and signal decay, to search for the member genes of the UvrY regulon, to identify the conserved functions of the various UvrY orthologs, and to screen libraries of small molecules with the intention of identifying antimicrobial agents that specifically target these systems. To address these questions we will primarily use E. coli as the model organism, and a wide array of biochemical and genetic techniques. Accomplishment of the goals should not only clarify the mechanisms of BarA-UvrY signal transduction and its scope of control, but could also improve our understanding of the integration of genetic circuits for bacterial adaptation to environmental changes, including those associated with host invasion during pathogenesis.

The BarA/UvrY of E. coli and its orthologs have been associated with phenotypes such as H2O2 detoxification, motility, biofilm formation and pathogenic interactions with both plant and animal hosts. However, thus far the E. coli system has been shown to activate transcription of only two genes: the small untranslated CsrB and CsrC RNAs, which has profound effects on carbon metabolism, motility and multicellular behavior of the cell. It is therefore, of highest importance to identify the genes regulated by this system, as the conserved functions of the various orthologs may become more evident. Also, it will facilitate the studies aimed at defining the DNA consensus-sequence for UvrY binding, which in turn will help our whole genome search for genes of the regulon that we may fail to identify with our experimental approaches. Finally, identification of the BarA/UvrY regulon will provide clues for the physiological signal(s) that stimulate the BarA sensor kinase activity. Accomplishment of our goals should not only clarify the mechanisms of BarA/UvrY signal transduction and its scope of control, but could also improve our understanding of the integration of genetic circuits for bacterial adaptation to environmental changes, including those associated with host invasion during pathogenesis. Two-component signal transduction systems, dependent on histidine and aspartyl residues as phosphoryl group donors and acceptors, play extensive roles in sensing environmental conditions. Although a few homologs have been found in yeast and higher plants, they are not known to exist in mammals. These systems are therefore considered potential targets for new families of drugs in infectious disease control. Also, better understanding of their structure and function should facilitate the design of specific inhibitors, and could also facilitate rational screening for novel drugs to treat infections.