Figure 4

Generation of a functional cysteine-free CadC by replacement of the disulfide bond forming cysteines with charged amino acids. Reporter gene assays were performed with E. coli EP314 (cadC::Tn10; cadA'::lacZ fusion) which was complemented with plasmid-encoded cadC or the indicated cadC derivatives. Cells were cultivated under microaerobic conditions in minimal medium at pH 5.8 or pH 7.6 in the presence or absence of 10 mM lysine at 37°C to mid-logarithmic growth phase, and harvested by centrifugation. The activity of the reporter enzyme β-galactosidase was determined [43] and served as a measurement for cadBA expression. Error bars indicate standard deviations of the mean for at least three independent experiments. Western blot analysis (inset - see Figure 1 for details) of all CadC derivatives (same order as in the graph) indicates production and membrane insertion.