FIG 5 .

Expression of the ktrAB operon. (A) Sequence alignment of the ktrAB promoter of the wild-type (WT) strain and three suppressor mutants (S1 to S3 mutations in strains GP2272 to GP2274, respectively). Conserved regions are underlined, and point mutations are highlighted in red. (B) The wild-type ktrA promoter region (strain GP2299) and the promoter regions of three ktrA promoter mutants (S1 to S3 mutations in strains GP2300, GP2714, and GP2701, respectively) were fused to lacZ. Bacterial cells were grown at the indicated potassium concentrations, and promoter activities were determined by quantification of β-galactosidase activities. Each circle represents the value for an individual biological replicate. The short horizontal bar represents the mean value (n = 4). (C) Determination of intracellular levels of KtrB labeled with a triple FLAG tag in the wild type (strain GP2277) and two different ktrAB promoter mutants (S1 and S3 mutations in GP2278 and GP2280 strains, respectively). Bacterial cells were grown at the indicated potassium concentrations, and KtrB was detected using antibodies recognizing the FLAG tag. The HPr protein served as the control (n = 3). The molecular weights (in kilodaltons) are shown to the left of the gels.