Figure 2

Mutations that enhance rtTA activity do not improve tTA activity. The transcriptional activity of tTA variants was measured in HeLa X1/6 cells [28] containing chromosomally integrated copies of the CMV-7tetO luciferase reporter construct. Cells were transfected with the tTA expression plasmids indicated or pBluescript (-) as a negative control and a plasmid constitutively expressing Renilla luciferase to correct for differences in transfection efficiency. Cells were cultured in the presence of different dox concentrations (0–20 ng/ml). The ratio of the firefly and Renilla luciferase activities measured two days after transfection reflects the tTA activity. All values were related to the original (wild-type) tTA activity in the absence of dox, which was arbitrarily set at 100%. Average values of two transfections are shown with the error bars indicating the standard deviations.