Transgenic construct used to study interactions between insulators and promoters. Consists of 10 UAS sites, an FRT cassette containing a mutant form of the Abd-B Fab-8 insulator (in which both of the CTCF binding sites have been mutated) in the forward orientation, the y coding region, a loxP cassette containing the mutant Fab-8 fragment in the forward orientation and the mini-w gene.