The pBS-KS-attB2-SA(0)-T2A-GAL4DBD-Hsp70 plasmid contains a recombination-mediated cassette exchange (RMCE) cassette that consists of two inverted attB sites which surround an intron phase 0 "Trojan GAL4DBD" cassette composed of a splice acceptor site followed by the T2A peptide, sequence encoding a GAL4(DBD)::Zip- hemidriver (component of the 'Split GAL4' system, contains the GAL4 DNA-binding domain) 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(DBD)::Zip- 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(DBD)::Zip- open reading frame. Thus the GAL4(DBD)::Zip- hemidriver should be expressed under the control of the regulatory sequences of the native Drosophila gene of interest in the resulting fly line.
One of 3 essentially identical plasmids (pBS-KS-attB2-SA(0)-T2A-GAL4DBD-Hsp70, pBS-KS-attB2-SA(1)-T2A-GAL4DBD-Hsp70 and pBS-KS-attB2-SA(2)-T2A-GAL4DBD-Hsp70) that vary only in the phase of the Trojan GAL4DBD cassette.