FIGURE 3.

Comparison of lac promoter activities in response to IPTG in lacZα, lacZ, and mCherry reporter systems. (A) Response curves of Top10/pPlac-lacZα, Top10/pPlac-lacZ, and Top10/pPlac-RFP to different concentrations of IPTG. Recombinant E. coli was first induced with 0–1 mM IPTG at 37°C for 8 h. Then, β-galactosidase activity and mCherry fluorescent signal of induced cultures were determined. (B) Time courses of reporter signals in recombinant Top10/pPlac-lacZα, Top10/pPlac-lacZ, and Top10/pPlac-RFP treated with 0.6 mM IPTG. Recombinant E. coli was induced with 0.6 mM IPTG, and β-galactosidase activity and mCherry fluorescent signal of induced cultures were determined at regular time intervals. The data are representative of three independent experiments and expressed as mean ± SEM. The optical density at 630 nm and the mCherry fluorescence intensity were all normalized by the OD₆₀₀ value of the induced culture.