FIG. 4.

ZntR^R19A does not activate zntA transcription. N-terminally six-His-tagged wild-type ZntR and ZntR^R19A were expressed from a pBAD promoter in the MC4100 zntR::cat derivative carrying the transcriptional zntA::lacZ fusion. Specific β-galactosidase activities were determined 30 min after induction of ZntR with arabinose (0.005% final concentration) in the presence (hatched bars) or absence (open bars) of ZnSO₄ (0.5 mM final concentration). The data are the averages of three independent cultures with a standard deviation of 0.001 in the absence of added zinc and 0.01 or 0.002 in the presence of added zinc expressing wild-type ZntR or ZntR^R19A, respectively.