The PBac{IRES-GFP.GT} 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, three stop signals (one in each frame), an internal ribosome entry site (IRES) and a promoterless EGFP coding sequence. At the other end of the element, a polyA trap cassette is present that consists of the w^IRES-GFP.GT minigene with its its own promoter but lacking a 3'-UTR and natural stop signal, followed by a splice donor site. The polyA trap cassette acts as a visible marker for a successful integration into a gene; w 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 mini-w gene containing its own promoter but lacking a 3'-UTR and natural stop signal, followed by a splice donor site.