FIG. 4.

Hfq is necessary for DsrA-mediated regulation of rcsA::lacZ, but Hfq does not regulate rcsA::lacZ alone. 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 a wild-type rcsA90::lacZ strain containing pDsrA (100%) (gray bars). Black bars represent the addition of 150 μM arabinose. pBADHfq expresses recombinant Hfq under control of the araBAD promoter. pDsrA has DsrA cloned into pACYC184 under control of its own promoter. The presence of the hfq-1 mutation in an isogenic wild-type strain is indicated.