Identification and Molecular Characterization of the Mg 2+ Stimulon of Escherichia coli

Abstract

ABSTRACT Transcription profile microarray analysis in Escherichia coli was performed to identify the member genes of the Mg 2+ stimulon that respond to the availability of external Mg 2+ in a PhoP/PhoQ two-component system-dependent manner. The mRNA levels of W3110 in the presence of 30 mM MgCl 2 , WP3022 ( phoP defective), and WQ3007 ( phoQ defective) were compared with those of W3110 in the absence of MgCl 2 . The expression ratios of a total of 232 genes were <0.75 in all three strains (the supplemental data are shown at http://www.nara.kindai.ac.jp/nogei/seiken/array.html ), suggesting that the PhoP/PhoQ system is involved directly or indirectly in the transcription of these genes. Of those, 26 contained the PhoP box-like sequences with the direct repeats of (T/G)GTTTA within 500 bp upstream of the initiation codon. Furthermore, S1 nuclease assays of 26 promoters were performed to verify six new Mg 2+ stimulon genes, hemL , nagA , rstAB , slyB , vboR , and yrbL , in addition to the phoPQ , mgrB , and mgtA genes reported previously. In gel shift and DNase I footprinting assays, all of these genes were found to be regulated directly by PhoP. Thus, we concluded that the phoPQ , mgrB , mgtA , hemL , nagA , rstAB , slyB , vboR , and yrbL genes make up the Mg 2+ stimulon in E . coli .