Fig. 6

Validation of the theophylline-responsive gene expression system with gus reporter gene. a SDS-PAGE analysis showed the expression level of GUS in the absence and presence of theophylline. The induced expression level of GUS in the recombinant strain, BSGgus, was determined by treatment with 8 mM theophylline for 20 h culture, and the culture treated with 4% DMSO for the same time after induction was designated as controls (0 mM). The solid triangle pointed the overproduced GUS. Protein extracts from B. subtilis 168 sampled simultaneously with the induced recombinant strains was used to be the negative control. GUS, denoted the purified GUS protein, was used to be a specific marker to indicate the bands of GUS on SDS-PAGE. b Enzymatic assay for GUS in BSGgus after induction by 8 mM theophylline for 16 and 20 h. The induced activities of GUS and the levels for leakage are shown by solid and open circles, respectively. The histograms represent the corresponding induction ratios. The enzymatic activity assay was performed in triplicates and the data are presented in mean ± SD