Transgenic construct in which y and w are used as reporters in an enhancer blocking assay; construct used to study the gypsy\su(Hw)BR insulator. Transgenic construct in which y and w are used as reporters in an enhancer blocking assay; construct used to study the gypsy\su(Hw)BR insulator. Contains a fragment bearing two copies of a 430bp gypsy\su(Hw)BR insulator sequence separated by a 1.5kb spacer, followed by the y coding region (including 5' regulatory sequence to -893bp relative to the y transcription start site). The spacer fragment is derived from the second exon of the y gene. The w+mC minigene is present downstream of the y coding region.