Table 1. Transcriptional activation by transiently transfected tetracycline-dependent transactivators.

Cell line	Plasmid transfected with	std. RLU		x-fold induction
	pUHC13-3	Doxy(–)	Doxy(+)
HeLa	pUHD172-1neo	2.72	335.31	123.2
	prTE 4d38-neo	1.22	38.25	31.4
Cos-7	pUHD172-1neo	29.4	1226.7	41.7
	prTE 4d38-neo	20.0	565.9	28.3
NIH 3T3	pUHD172-1neo	8.75	687.8	78.6
	prTE 4d38-neo	2.52	132.1	52.4

pUHC13-3 and pRL-CMV (Renilla luciferase expression vector) were co-transfected with pUHD172-1 or prTE4d38 into 1–3 × 10⁵ cells. Cultures were incubated in the presence or absence of doxycycline for 24 h before luciferase activity was measured and standardized to Renilla luciferase activity. Induction ratios were estimated by standardized basal levels of luciferase activities [std. RLU, Doxy(–)] and standardized induced levels of luciferase activities [std. RLU, Doxy(+)]. Doxy(+) or (–), presence or absence of doxycycline, respectively. Results were the average from three experiments.