Mutants affected in alkaline phosphatase, expression: evidence for multiple positive regulators of the phosphate regulon in Escherichia coli.

The expression of alkaline phosphatase (the product of the phoA gene) in Escherichia coli is believed to be subject to both positive control by the phoB gene product and negative control by the phoR gene product. We have isolated a large number of PhoA- mutants in the phoR- genetic background. Among mutants altered in the positive control of alkaline phosphatase, some were phoB mutants; others had a mutation in a new gene, designated phoM. We believe that the phoM gene codes for a positive regulator that acts together with the phoB gene product in phoA gene expressions.--The phoM phenotype was found to be masked in phoR+ strains. This and other evidence support a positive regulatory role for the phoR gene product as well.--Our experiments demonstrate that phoA is under positive control by three different positive regulators: the product of the phoB, phoM and phoR genes. The phoB gene product is always needed together with either the phoR or phoM gene product. In addition, the phoR gene product acts as a negative regulator.--We describe a model for phoA gene expression consistent with this new evidence.