Fig. 5. FACS analysis of transfected S2 cells. Density plots of yellow versus cyan fluorescence intensity for S2 cells co-transfected with metallothionein-Gal4 and various plasmids, obtained 12 h after cupric sulfate induction. The flow cytometer detection optics are inherently less sensitive for CFP than for YFP. 50 000 cells were observed on each plot. (A) Mock-transfected S2 cells show minimal cyan or yellow fluorescence. (B) U2Y-transfected cells show only yellow fluorescence. (C) U2C-transfected cells show only cyan fluorescence. (D) U2C–U12Y-transfected cells show greater cyan than yellow fluorescence (correcting for low CFP detection sensitivity). (E) U12C–U2Y-transfected cells show greater yellow than cyan fluorescence.