Isolation and Molecular Characterization of the Locked-on Mutant of Mg²⁺ Sensor PhoQ in Escherichia coli

抄録

A Mg²⁺ sensor mutant (PhoQD179L(A)) in which D179 of PhoQ was changed into L or A was isolated and characterized in Escherichia coli. PhoQ–PhoP regulon genes, phoPQ, mgtA and mgrB transcriptions were repressed at a high Mg²⁺ concentration in WQ3007 (phoQ-defective strain)/pHO119, but not in WQ3007/pHO179L(A). The in vitro autophosphorylation activity of membrane-bound PhoQ was repressed by Mg²⁺ (10 mM), but that of membrane-bound PhoQD179L(A) was not. Furthermore, the phosphotransfer from membrane-bound PhoQ to PhoP was also repressed by Mg²⁺, but was not observed in membrane-bound PhoQD179L(A). These results suggest that PhoQD179L(A) is a locked-on mutant that is defective in extracellular Mg²⁺-sensing and that the D179 amino acid residue of PhoQ plays an essential role in signal transfer between the Mg²⁺-sensory and histidine kinase domain of PhoQ.