FIG. 3.

Feedback derepression in a strain overexpressing rpoA-R265A. Promoter activities in strains overexpressing rpoA-R265A (from pHTf1-αR265A) were compared to activities in strains overexpressing wild-type α (pHTf1-αWT) using promoter-lacZ fusions described in Fig. 1 and 2. Promoter activity is expressed relative to the average activity measured in strains overexpressing wild-type α. Promoter activities in strains overexpressing wild-type α were as follows: rrnB P1, 60 MU; lacUV5, 808 MU; and rrnB P1(dis), 762 MU. Strains were grown as described in the legend to Fig. 2, with the addition of 100 μg of ampicillin/ml. ATP and ppGpp concentrations were measured as described in the legend for Fig. 2. Nucleotide concentrations are expressed relative to the concentration in the strain overexpressing wild-type α. The growth rates of the strains expressing the wild-type and mutant α were 0.84 and 0.65 doublings/hour, respectively.