Fig. 3. Conversion of a multiple state element to a binary on/off switch. Two additional Giant (gt) binding sites were introduced at the 3' end of the Gal4 activator cluster. (A,B) As observed previously, Dorsal/Twist (dl/twi) activators are repressed in anterior and posterior regions of Giant expression (arrows). (C,D) In the presence of Dorsal/Twist and Gal4 activators, complete repression of transcription is observed in areas of Giant expression (arrows). Embryos are oriented anterior to the left. Lateral (A,C) and ventral (B,D) views are shown.