The P{Wee-P.un} entry in FlyBase is used to denote the transgenic construct present when one of P{Wee-P.ph0}, P{Wee-P.ph1} or P{Wee-P.ph2} has been inserted into the genome, but it is not known which intron phase variant the inserted element corresponds to. The element is composed essentially of an artificial exon that consists of a splice donor site, the EGFP coding sequence (with its ATG codon and a consensus translation initiation sequence just 5' to the ATG) 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 intron phase. The presence of the translation start sequence means that insertions into the 5'UTR of an endogenous gene may act as a promoter trap, also resulting in EGFP expression. A single FRT site is present 5' to the protein trap cassette.