The Mi{Trojan-GAL4.un} entry in FlyBase is used to denote the transgenic construct present in an insertion when it is known that the inserted element corresponds to one of Mi{Trojan-GAL4.0}, Mi{Trojan-GAL4.1} or Mi{Trojan-GAL4.2}, but it is not known which of these 3 intron phase variants the inserted element corresponds to. The Mi{Trojan-GAL4.un} element is generated in vivo by using phiC31:int-mediated recombination to replace the attP cassette of a Mi{MIC} element insertion with a 'Trojan GAL4' cassette. The Trojan GAL4 cassette consists of a splice acceptor site followed by the T2A peptide, the GAL4 coding sequence and an Hsp70 transcription termination signal. Integration of the cassette into a Mi{MIC} insertion in 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.