FIG. 3.

Dependency of β-lactamase induction on the activity of LTs. Expression of β-lactamase from pJP1 (ampC ampR) by cefoxitin (4 μg/ml) was determined in E. coli with different levels of active LTs. To vary the intracellular concentrations of active Slt70 and MltB, respectively, either the Slt70-specific inhibitor bulgecin was added (50 μg/ml) or MltB was overproduced by induction of expression from plasmid pAU1 by the addition of IPTG (isopropyl-β-d-thiogalactopyranoside) (10 μg/ml) as described in Materials and Methods. Hydrolysis of nitrocefin by crude cell extracts (10 μg of protein) was measured as described in Materials and Methods. The change in absorbance at 492 nm is shown. Solid circles, IPTG and cefoxitin; solid triangles, cefoxitin; solid squares, IPTG; crosses, bulgecin and cefoxitin; open circles, control; open squares, bulgecin.