The pBS-KS-attB2-SA(2)-T2A-Gal4-Hsp70 plasmid contains a recombination-mediated cassette exchange (RMCE) cassette that consists of two inverted attB sites which surround an intron phase 2 "Trojan GAL4" cassette composed of a splice acceptor site followed by the T2A peptide, the GAL4 coding sequence and an Hsp70 transcription termination signal. In the presence of phiC31:int integrase, the attB cassette can undergo RMCE with a target in the genome that contains inverted attP sites, such as the Mi{MIC} element, replacing the target attP cassette with the donor attB cassette sequence. 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 fly line.