The P{PTT-un} entry in FlyBase is used to denote the transgenic construct present when one of P{PTT-GA}, P{PTT-GB} or P{PTT-GC} has been inserted into the genome, but it is not known which intron phase variant the inserted element corresponds to. The P{PTT-un} 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.