P{lox(Trojan-GAL4)x3} is a transgenic donor construct containing three tandem 'Trojan GAL4' cassettes, one in each intron phase. The Trojan GAL4 sequence in each case consists of a splice acceptor site followed by the T2A peptide, the GAL4 coding sequence and an Hsp70 transcription termination signal. Each cassette is flanked by attB sites nested within a pair of uniquely compatible lox sites (lox2272 for the phase 0 cassette, loxN for the phase 1 cassette, and loxP for the phase 2 cassette). Expression of P1cre recombinase will excise and circularise all three cassettes, which can then be integrated into the attP sites of a Mi{MIC} insertion using phiC31:int integrase. Integration of the cassette with the appropriate phase into a coding intron of a native Drosophila gene of interest will result in the cassette behaving as a 'Trojan' exon: the splice acceptor site ensures that the T2A-GAL4 open reading frame is incorporated into the mRNA of the native Drosophila gene, while the T2A sequence truncates the native gene product and promotes the separate translation of the GAL4 open reading frame. Thus GAL4 should be expressed under the control of the regulatory sequences of the native Drosophila gene of interest in the resulting Trojan-MiMIC GAL4 driver line.