SulA turnover in a Δlon strain in the presence of mutant Lon protein. Strains were grown in LB medium supplemented with 1% arabinose to an OD600 of 0.2–0.3. Cells were UV irradiated at 15–20 J/m2. After 20 min of growth to allow SulA induction, spectinomycin was added at a final concentration of 150 μg/ml. One milliliter of culture was removed at the times indicated and TCA-precipitated. Proteins were separated by SDS/PAGE, and Lon was detected by Western blot, as described in Materials and Methods. (A) SulA turnover in a Δlon ftsZ+ host. Percent of SulA remaining as a function of time after blocking protein synthesis with spectinomycin. Strains were SG22569 (Δlon ftsZ+) containing either pBAD24 (●), pBADlonK362Q (□), pBADlonS679A (○), or pBADlonK362Q-S679A (▴). The dotted line shows the previously observed degradation of SulA in a lon+ host (16, 33). SulA was not detected in the lon+ host in these experiments. (B) SulA turnover in a Δlon sfiB* host. As for A, but strains were LVM806 (Δlon sfiB*) containing either pBAD24 (●) or pBADlonS679A (○).