FIG. 2.

Feedback derepression in a nusB5 strain. Promoter activities in wild-type and nusB5 strains were measured from single-copy promoter-lacZ fusions using β-galactosidase assays. Promoter activities are expressed relative to the average activity measured in a wild-type strain. Absolute promoter activities in the wild-type strain were as follows: rrnB P1, 96 Miller units (MU); lacUV5, 1,519 MU; rrnB P1(dis), 1,295 MU. Strains were grown at 37°C in morpholinepropanesulfonic acid (MOPS) minimal medium supplemented with 0.4% glucose, 10 μg of thiamine/ml, and 1 mM KH₂PO₄. ATP and ppGpp were extracted from identical cultures grown in the presence of 20 μCi of KH₂³²PO₄/ml. Nucleotide concentrations are expressed relative to the concentration in the wild-type strain. Error between measurements from independent cultures is indicated. The growth rates of the wild-type and mutant strains were 1.20 and 0.73 doublings/hour, respectively.