Fig. 1

Comparison of the induced efficacies of twelve Tet-on plasmids. a Comparison of two transactivators. Both TetON3G and rtTA3 were fusions of TetR and several VP16-derived minimal ADs. TetR is composed of a DNA binding domain (BD) and a core domain following a dimerization surface. The F67S, R171K (red arrow), and S12G (blue arrow) mutations of amino acids are indicated. b Comparison of three TREs: TRE3Gs, TRE3Gp, and TetO6. These TREs contain seven (TRE3Gs and TRE3Gp) or six (TetO6) TetOs with a 36-bp center-to-center distance. Moreover, they have TFIIB and a TATA box, as well as a predicted initiator (Inr), but differ in the length and composition of the 5′-UTR sequence. T: TetO6. c Schematic representation of different combinations of two transactivators, three TREs, and two orientations (the same and the opposite) of inducible expression cassette. d The induced efficiency of 12 Tet-on plasmids (p1-p12). HEK293A cells were transfected with each of the 12 plasmids with firefly luciferase as a reporter gene. Cells were grown in the absence or presence of 1 μg/mL Dox. After 48 h, cells were harvested for a luciferase activity assay. Firefly luciferase activity was normalized to Renilla luciferase activity. e The fold induction of the 12 plasmids. Fold induction was defined as the ratio between the induced expression level with Dox and the background expression level without Dox