Fig. 1. Transposon constructs. (A) The YGfPfMG construct is shown schematically with the PRE, gypsy, miniwhite and the yellow gene as a marker. FRT sites flanking the PRE allow its excision in the presence of the FLP enzyme, to give YGfMG. (B) The LexA-PC and the GAL-TRX expression constructs: the expression is driven by the hsp70 promoter and the yellow gene serves as a marker. (C) BHL4G4 contains LexA and GAL4 binding sites. The expression of the Ubx-lacZ gene is directed by the embryonic BX enhancer and the 2212H1 imaginal disc enhancer of Ubx. The marker gene is miniwhite. In BHL4G4PRE, the bxd PRE is added. The arrows indicate the direction of transcription. The yellow, lacZ and trx genes are not shown to scale.