Wanner 9730034 Cross regulation is the regulatory interactions that occur between different global systems. These interactions may be key information integrators, directly linking different pathways in a network to coordinate growth and metabolism. The most compelling evidence for cross regulation is found in the phosphate (Pho) regulon of E. coli. The Pho regulon is comprised of a large number of co-regulated genes encoding uptake systems and degradative enzymes required for the use of various environmental phosphorus (P) sources. This system is controlled primarily by the PhoR/PhoB two-component regulatory system; its control responds to the extracellular inorganic phosphate (Pi) level and is coupled to a Pi transporter but not Pi uptake per se, the first step of Pi metabolism. Cross regulation of PhoB involves two additional signal transduction pathways that are coupled to the incorporation of Pi into ATP, the primary phosphoryl donor in metabolism. One signaling pathway leads to activation of PhoB by the catabolite regulatory sensor kinase CreC (formerly called PhoM). CreC and its partner response regulator are thought to control genes of central metabolism, although no target gene was previously known. The other leads to activation of PhoB by acetyl phosphate, an intermediate of the phosphotransacetylase-acetate kinase (Pta-AckA) pathway of substrate level phosphorylation for entry of Pi into ATP. Accordingly, cross regulation links the control of genes for P assimilation with those for central carbon and energy metabolism. New genetic tools have been developed to identify genes controlled by a regulatory protein of unknown function. These tools were used to identify CreC/CreB-regulated genes. One such gene is especially interesting as it encodes a protein that is highly conserved in diverse bacteria (E. coli, Haemophilus influenzae, Bacillus subtilis, and Methanococcus jannaschii), suggesting an important, although unidentified, function. Other recent results suggest that high energy com pounds in addition to acetyl phosphate are involved in the in vivo activation of PhoB. New studies have been designed to further investigate these results. Specific Aim 1 is to define the genetic regulation of the newly identified CreB-regulated (cbr) genes and, as feasible, to identify additional cbr genes using similar or new strategies, including ones based on genomic techniques. Specific Aim 2 is to define the function of one or more cbr genes using newly developed genetic and genomic techniques. Specific Aim 3 is to define the role of one or more high energy compounds in global regulation of gene expression using similar approaches. These studies will be valuable both in gaining a deeper understanding of cross regulation and the control of genes in central metabolic pathways in bacteria and in developing strategies for studying global regulation of gene expression in the new era of bacterial genomics.
