Analysis of regulation of phoB expression using a phoB-cat fusion

The phoB gene, which encodes a positive control factor for a number of phosphate-regulated genes in Escherichia coli, was cloned into multicopy plasmid pBR322. A phoB-cat fusion that expressed chloramphenicol transacetylase from the phoB promoter was constructed. Studies of the expression of the phoB-cat fusion showed that the pattern of regulation of the phoB gene was similar to that of the phoA gene, the structural gene for alkaline phosphatase. The phoB gene was derepressed under conditions of phosphate starvation, was constitutively expressed in a phoR background, and required the phoM gene product for expression in a phoR strain. Finally, a functional phoB product was required for its own synthesis. Our results indicate either that phoA gene expression responds directly to the concentration of the phoB gene product in cells or that the phoA and phoB controlling elements are quite similar.