Fig. 3. (A-H) The sal flight appendage-specific cis-regulatory element is directly repressed in the haltere by Ubx. Nomarski photomicrographs of third larval instar wing (A,C,E,G) and haltere (B,D,F,H) imaginal disks assayed for ß-galactosidase activity driven by various elements in transgenic animals carrying reporter constructs. In these panels, anterior is to the left and ventral is to the top. (A) The sal 1.1 element drives reporter activity in the wing field straddling AP boundary. (B) No sal 1.1 element driven reporter activity is seen in the haltere (arrowhead). (C) Mutation of all seven Ubx binding sites in the sal 1.1 u1-7 element does not alter the pattern of reporter activity in the wing. Therefore, the abilities of trans-activating factors required to activate the sal 1.1 element have not been affected by the mutations. (D) Mutating all seven Ubx binding sites in the sal 1.1 u1-7 element results its dramatic derepression in the haltere, as indicated by its ability to drive strong ß-galactosidase activity in a pattern very similar to that in the wing. (E) The sal 328 element drives wing-specific reporter activity in a pattern complementary to that of the sal 1.1 element. (F) No reporter activity driven by this element is present in the haltere. (G) The mutant sal 328 u5-7 element in which the three Ubx binding sites were abolished drives ß-galactosidase activity in the wing in a pattern largely similar to that driven by the wild-type sal 328 element. We note that reporter activity driven by the mutant element is expanded towards the AP boundary compared to that driven the wild-type one. This may have occurred because the Ubx binding site mutations in the sal 328 u5-7 element also affected binding sites for other transcription factors that regulate it. (H) The mutant sal 328 u5-7 element drives reporter activity very strongly in the haltere.