FIG. 4.
Effect of various E. coli proteases on EDF production. (A) Supernatants of dense cultures of E. coli MC4100relA1 (WT), MC4100relA1 ΔclpP (ΔclpP), MC4100relA1ΔclpA (ΔclpA), MC4100relA1ΔclpX (ΔclpX), and MC4100relA1Δlon (Δlon) grown to mid-logarithmic phase (OD600 of 0.6) were prepared (see legend to Fig. 2), and EDF activities were quantified (see Materials and Methods). (B) Strains were as in panel A, but each of them harbored pQE-mazF to allow the overproduction of MazF (+MazF). These strains were grown in M9 with ampicillin to mid-logarithmic phase (as described for panel A). Cells were washed with and resuspended in prewarmed M9 and incubated without shaking at 37°C for 10 min. To induce mazF, IPTG (1 mM) was added, and the cells were incubated without shaking at 37°C for an additional 30 min. Supernatants were obtained from these cells as described for panel A.