The PBac{GT1} element contains two trapping cassettes. At one end of the element there is a mutagenic gene trap cassette consisting of an artificial splice acceptor site, a promoterless GAL4 driver coding sequence and an Hsp70 poly(A) signal. Upon integration into the genome, the GAL4 coding sequence can be transcribed as a fusion mRNA with an upstream exon sequence. A 'stop-start' sequence is placed between the splice acceptor site and the GAL4 coding sequence to ensure that the open reading frame of GAL4 is maintained in any integration event. At the other end of the element, a polyA trap cassette is present that consists of the Autographa californica nuclear polyhedrosis virus immediate-early promoter supplemented with the hr5 enhancer, EGFP coding sequence that lacks a poly(A) signal and an artificial splice donor site. This polyA trap cassette acts as a visible marker for a successful integration into a gene; EGFP is only stably expressed when a poly(A) tail is added by forming a fusion transcript with 3' exon(s) of the trapped host gene. A Disc\RFP^DsRed2.3xP3 marker is present between the two trapping cassettes.