Figure 1. Regulation of arnB.

The arnB-uidA fusion of strain A5256 was assayed in the presence of increasing concentrations of polymyxin (A), protamine (B), and Mg²⁺ (C). Effect of phoP and pmrA mutations on arnB-uidA regulation by Mg²⁺ (D) and protamine (E) was assayed. Cultures were performed in LB medium for A, C and D and in M63 medium for B and E since protamine precipitates in LB medium. Activities are the mean value from at least four separate experiments and are expressed in µmoles of p-nitrophenol produced per minute and per milligram of bacterial dry weight ± standard deviation.