Fig. 3

The activation of GFP expression by the P43′-riboE1 element displayed dose-dependency. a The expression levels of GFP induced by 1, 2, 4, or 8 mM theophylline were determined 24 h after induction, and were linearly correlated. The experiment was repeated independently in triplicates. b The activation ratios were estimated after induction of 1, 2, 4, or 8 mM theophylline. The ratios were elevated in response to the increased theophylline levels. The highest activation ratio was achieved by 8 mM theophylline, which caused an approximately sevenfolds increase. c SDS-PAGE analysis of with increasing amounts of theophylline. The black solid arrow indicates the GFP band. Twenty micrograms of total protein were loaded for each sample. The GFP fluorescence was measured in triplicates and the data were shown in mean ± SD