FIGURE 4.
In vivo activity and relative expression levels of PhoQ. A, E. coli strain CSH26ΔQ/F′lacIQkan, containing the pNL3 reporter plasmid and pLPQ2 for expressing the wild-type and mutant PhoQ proteins, were assayed for β-galactosidase activity following growth in N-media (0 μm MgCl2) or as supplemented with 40 μm or 10 mm MgCl2. Specific activity is shown in Miller units. Standard deviations are <10% of the mean, calculated from at least three individual experiments. B, the relative expression levels of the wild-type and mutant PhoQ proteins are shown by Western blotting, probed using an antibody specific for the cytoplasmic domain of PhoQ. The PhoQ variants are labeled above each lane accordingly. The control is the E. coli strain containing the “empty” pLPQ2 vector lacking the phoP-phoQ operon.