Transcription initiated on the Ef1 promoter suppresses the enhancer activity, while the SV40 transcriptional terminator protects the enhancers from the repressive effect of transcription. (A) (EF1)Ey(e)YW, the Ef1 promoter drives transcription through eye enhancer. (B) (EF1)(Ey)∆W∆Y, the Ef1 promoter drives transcription through yellow enhancers. (C) UAS(Ts)Ey(e)∆YtsW, the 702-bp SV40 terminator (Ts) is inserted between the UAS promoter and the eye enhancer. (D) (UAS)Ts(Ey)∆W∆Y, the 702-bp SV40 terminator is inserted between the UAS promoter and yellow enhancers. For other designations, see Figures 1 and2.