FIG. 3.

DsrA and Hfq are both needed for regulation of RpoS::LacZ at 30°C. Cultures of the various strains grown overnight were diluted 1:100 in LB broth. Cultures were grown at 30°C, and samples were taken at various times during logarithmic growth (0.2 > OD₆₀₀ < 1.0). Total β-galactosidase units were plotted against the OD₆₀₀ of the culture. The slopes of the curves between OD values of 0.2 and 1.0 (approximately log phase) were used as the specific activities of the fusions. Slopes had an r² of >0.95. Specific activities varied less than 10% between experiments. All activities are in relation to that of the wild-type RpoS::LacZ strain during logarithmic growth (100%) (gray bars). Black bars represent the addition of 150 μM arabinose. pBADHfq expresses recombinant Hfq under control of the araBAD promoter. The vector is the araBAD promoter vector pBAD24. pDsrA has DsrA cloned into pACYC184 under control of its own promoter. The presence of hfq-1 and dsrA1 mutations in isogenic strains is indicated. The inset above the bar graph is a Western blot of those strains using anti-Hfq antibody. Lanes 1 to 3 of the gel correspond to the strains and conditions immediately below the inset. Note the induction of Hfq after the addition of arabinose.