P{loxP(Trojan-GAL4.2)} is a transgenic donor construct containing a single 'Trojan GAL4' cassette, in intron phase 2. The Trojan GAL4 sequence consists of a splice acceptor site followed by the T2A peptide, the GAL4 coding sequence and an Hsp70 transcription termination signal. It is flanked by attB sites nested within a pair of loxP sites. Expression of P1cre recombinase will excise and circularise the cassette, which can then be integrated into the attP sites of a Mi{MIC} insertion using phiC31:int integrase. Integration of the cassette into a coding intron (with the same phase) 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.