Molecular genetic analysis of the Escherichia coli phoP

We have cloned the Escherichia coli phoP gene, a member of the family of environmentally responsive two-component systems, and found its deduced amino acid sequence to be 93 % identical to that of the Salmonella typhimurium homolog, which encodes a major virulence regulator necessary for intramacrophage survival and resistance to cationic peptides of phagocytic cells. The phoP gene was mapped to kilobase 1202 on the Kohara map (25-min region) of the E. coli genome (Y. Kohara, K. Akiyama, and K. Isono, Cell 50:495-508, 1987) and found to be transcribed in a counterclockwise direction. Both E. coli and S. typhimurium phoP mutants were more sensitive than their isogenic wild-type strains to the frog-derived antibacterial peptide magainin 2, suggesting a role for PhoP in the response to various stresses in both enteric species. Bacteria modulate expression of their genes in response to environmental changes. This modulation is frequently con-trolled at the transcriptional level by members of the family of two-component systems, in which a membrane-bound sensor-transmitter can detect changes in the environment, such as changes in osmolarity or concentrations of essential nutrients, and mediate the phosphorylation-dephosphoryla