Fig. 1. Two mechanisms that specify enhancer and promoter interaction in transgenic Drosophila. Schematic diagram of transcriptional interactions between AE1 and IAB5 enhancers and promoters in transgenic Drosophila. Transgenes are shown to contain AE1 or IAB5 (yellow rectangle) between divergently pointed promoter-reporter fusion genes (red and blue boxes). Direction of transcription and the position of start site are indicated by the arrows. Activating interactions between promoter and the enhancers are represented by arched arrows. Core promoter elements of eve and white are indicated underneath each promoter. The size and distance of the DNA elements are not to scale. (A) AE1 and IAB5 preferentially activate transcription from the evenskipped (eve) promoter which contains TATA, but not from the white promoter which contain initiator (INI) and DPE, but not TATA sequences. (B) AE1 and IAB5 can activate the white gene if the TATA region in the eve promoter is changed to the corresponding region from the white promoter. (C) AE1-eve interaction is completely blocked by the suHw insulator (red oval), with a redirection of transcription activation to the white promoter.