Molecular Characterization of the PhoP-PhoQ Two-Component System in Escherichia coli K-12: Identification of Extracellular Mg 2+ -Responsive Promoters

Abstract
We identified Mg2+-responsive promoters of thephoPQ, mgtA, and mgrB genes ofEscherichia 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.