TI{CRIMIC.TG4.1} represents a DNA segment that has been inserted into the genome by homology directed repair using CRISPR/Cas9 in combination with a donor plasmid based on pM37_p1. The inserted TI{CRIMIC.TG4.1} DNA is not flanked by transposable element ends and consists of a recombination-mediated cassette exchange (RMCE) cassette flanked by a pair of inverted attP sites. Inside the attP sites is a cassette flanked by a pair of direct FRT sites. This in turn contains an intron phase 1 'Trojan GAL4' gene trap element (composed of a splice acceptor site followed by the T2A peptide, the GAL4 coding sequence and an SV40 polyadenylation signal), followed by the Avic\GFP^3xP3.cLa marker allele. Integration of TI{CRIMIC.TG4.1} 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-CRIMIC GAL4 driver line. In addition, the presence of the inverted attP sites allows for the entire RMCE cassette sequence to be replaced with DNA from a compatible donor plasmid (where the sequence to be inserted is flanked by inverted attB sites) through recombination-mediated cassette exchange (RMCE) driven by the phiC31:int integrase.