Transgenic construct used to study interactions between insulators and promoters. Consists of 10 UAS sites, an FRT cassette containing a 254bp fragment of the Abd-B Fab-8 insulator (containing the two CTCF binding sites - nucleotides 64038 to 64291 in clone DS07696) in the forward orientation, the y coding region, a loxP cassette, containing the 254bp Fab-8 fragment in the reverse orientation and the mini-w gene.