Fig. 1. The Ubx PRE indiscriminately silences reporter genes that contain an enhancer and a TATA box minimal promoter. (Left) Schematic drawing of the reporter constructs that contain the 1.6 kb Ubx PRE fragment (hatched rectangle) flanked by FRT sequences upstream of either the vg^QE, vg^BE or dpp^WE enhancer (black rectangle) linked to hsp70 TATA box minimal promoter (white circle) followed by hsp70 5' UTR (thin line) and lacZ gene (white box). A transgene derivative that lacks the PRE (below) can be created by flp-mediated excision of the PRE fragment. (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. In the absence of the PRE fragment, the vg^QE, dpp^WE and vg^BE enhancer each direct lacZ expression in the pattern previously described (Williams et al., 1994; Kim et al., 1996; Müller and Basler, 2000). The pattern directed by the vg^BE enhancer depends on its relative orientation to the TATA box promoter; in this orientation it activates expression primarily in the hinge and notum region (Williams et al., 1994). Note that in the presence of the PRE fragment, all three reporter genes are completely silenced.