The P{PTT-GB} construct contains an artificial exon that consists of a splice donor site, a multiple tag cassette (Tag:polyHis followed by EGFP without start and stop codons), and a splice acceptor site. The exon is designed to act as a protein trap element when inserted into a coding intron of an endogenous gene in the correct orientation and splice phase.

In addition to acting as a protein trap element, insertions of the P{PTT-GB} element may also act as enhancer trap lines. This can occur via the production of a mRNA in which the artificial EGFP exon is fused to sequences derived from the non-coding strand of the mini-w marker present at the 5' end of the construct (this sequence contains a cryptic start codon and is in a compatible frame with the EGFP coding sequence in P{PTT-GB}). Insertions that act as enhancer traps rather than protein traps are typically located upstream of the annotated start site of the trapped gene and the EGFP protein produced is localized to the nucleus, possibly due to fusion of the first exon of P\T gene sequence present in the construct to the EGFP coding sequence.