Molecular characterization of the PhoP-PhoQ two-component system in Escherichia coli K-12: identification of extracellular Mg2+-responsive promoters

We identified Mg2+-responsive promoters of the phoPQ, mgtA, and mgrB genes of Escherichia coli K-12 by S1 nuclease analysis. Expression of these genes was induced by magnesium limitation and depended on PhoP and PhoQ. The transcription start sites were also determined, which allowed us to find a (T/G)GTTTA direct repeat in their corresponding promoter regions.