Transgenic construct used to study interactions between boundary elements from the bithorax complex. Consists of 10 UAS sites, an FRT cassette containing a 375bp fragment from upstream of the Abd-B promoter that includes a CTCF protein binding site (in forward orientation relative to the w gene), the y transcription unit, a loxP cassette containing a 337bp fragment consisting of 83bp from the PTS (promoter-targeting sequence) and 254bp of the Fab-8 element, in which the CTCF protein binding sites have been mutated (the fragment is in reverse orientation relative to the w gene), and a w minigene. The UAS sites are at -893bp relative to the y transcription start site, and at a distance of almost 5kb relative to the w transcription start site.