Analysis of the conserved acidic residues in the regulatory domain of PhoB.

The PhoB protein from Escherichia coli is a member of the two-component signal transduction pathway that controls an adaptive response to limiting phosphate. Activation involves its phosphorylation on a conserved aspartate. Site-directed mutations were introduced at conserved acidic residues. The E9D, D10E, D10N, E11A, E11D and E11Q mutants were each able to induce alkaline phosphatase under low phosphate growth conditions whereas the E9A, D10A, D53A, D53E and D53N could not. The E9Q mutant was constitutively active. Phosphorylation assays showed that only the E9D, E11A, E11Q and E11D mutants were phosphorylated by acetyl phosphate. Most mutants also displayed defects in magnesium binding.