Fig. 3.

Effects of ppGpp and DksA on the ompA gene expression (a) and the pB promoter activity (b, c). Wild-type (WT) E. coli or ppGpp⁰ (relA spoT double mutant), DksA⁰ (dksA::kan mutant) and ppGpp⁰ DksA⁰ (relA spoT dksA triple mutant) strains were cultured in the LB medium at 37°C to exponential (a and exp in b) or stationary (st in b) phase of growth. Primer extension experiments were performed as described in “Materials and methods”, and the products of the reactions were separated during polyacrylamide gel electrophoresis, with the products of the sequencing reaction (performed using the same primer) run at the same gel (lanes G, A, T and C). a and b show representative autoradiograms (positions of the products of primer extension reactions, corresponding to transcripts originating from ompA and pB promoters, are shown). c demonstrates quantification (by densitometric analysis) of the results exemplified in b (mean values from three independent experiments are shown in c with error bars indicating SD)