FIG. 4.
Expression and σS dependence of gadA::lacZ and gadB::lacZ fusions under different growth and stress conditions. Strains JK86 and JK87, which carry transcriptional single-copy lacZ fusions in gadA and gadB (black and hatched bars, respectively), as well as their rpoS::Tn10 derivatives (grey and white bars, respectively) were grown in LB medium. During log-phase growth, an aliquot of the culture was shifted to pH 5 (see Materials and Methods for details). Samples were taken during log phase (OD578 = 0.4; pH 7), 40 min after shift to pH 5, and during entry into stationary phase (OD578 = 4; pH 7). Specific β-galactosidase activities were measured (the data given represent the average of three independent experiments each).