Fig. 2. The Ubx PRE indiscriminately silences reporter genes that contain an enhancer and the Ubx proximal promoter. (Left) The reporter genes are very similar to those shown in Fig. 1 but the TATA box minimal promoter is replaced by a 4.1 kb fragment that contains the proximal Ubx promoter and 5' UTR (thin line, transcription start site marked by arrow). (Right) X-gal staining of wing imaginal discs from transformant lines carrying the indicated reporter gene construct with (left column) and without (right column) the PRE fragment; in each case, the disc on the left is from the original transformant line and the disc on the right is from its derivative line, obtained after excision of the PRE in the germline. Note that in the presence of the PRE fragment all three reporter genes are completely silenced. In the derivative lines lacking PRE, the intensity of X-gal staining suggests that the vg^QE enhancer directs higher expression levels from the Ubx promoter than from the TATA box promoter; conversely, the dpp^WE enhancer activates expression more potently from the TATA box promoter than from the Ubx promoter (compare with Fig. 1).