Fig. 5. PmrD acts downstream of the PhoP–PhoQ system and upstream of the PmrA–PmrB system. β-galactosidase activities (Miller units) expressed by transformants grown in N-minimal medium pH 7.7 with 10 µM Mg²⁺ (A) or 10 mM Mg²⁺ (B) were determined for mutants harboring a lac transcriptional fusion to pbgP. The transcriptional activity was determined in six genetic backgrounds: wild type, phoQ, phoP, pmrD, pmrB and pmrA. The strains were transformed with a plasmid harboring the pmrD gene expressed from the lac promoter (pLK24) or the cloning vector (pUC19). The data correspond to mean values of four independent experiments performed in duplicate. Error bars correspond to the standard deviation (and are only shown if greater than the resolution of the figure).