Figure 6.

RecQ is required for proper SOS induction in response to DNA replication interference. (A) Expression of the umuDC::lacZYA fusion gene in the dnaE486 strain grown at the semirestrictive temperature. Overnight cultures of wild-type cells, ΔrecQ, dnaE486, or dnaE486 ΔrecQ mutants were grown at 30°C, diluted into fresh LB medium, and incubated at 38°C. Aliquots were sampled at specific intervals and examined for β-galactosidase activity. Values are averages of the enzyme activities in Miller units of duplicate samples measured after the shift to 38°C. (B) Effect of recQ mutation on UV-induced LexA degradation. Measurements of LexA degradation were performed as described in Materials and Methods. The cells were UV-irradiated (time 0), and aliquots were sampled at intervals. Samples were analyzed by 15% SDS-PAGE, and RecA and LexA proteins were detected by immunoblotting with anti-RecA and anti-LexA antibodies. The reproducibility of the data was confirmed by four independent experiments. (C) The relative amounts of LexA protein shown in B were plotted after they were normalized to the values at time zero. (Open circles) Wild type; (filled circles) recQ61::Tn3; (open squares) uvrA6; (filled squares) uvrA6 recQ61::Tn3.