Transgenic construct used to study the properties of the Fab-7 insulator, by analyzing its effects on y and w expression in an enhancer blocking assay. Contains a 3kb SalI-BamHI fragment of the y regulatory region that contains the wing and body enhancers (nucleotides -2873 to -1266 relative to the transcription start site), fused upstream of a 5kb BamHI-BglII fragment containing the y coding region. The w eye enhancer (nucleotides -1465 to -1084 relative to the transcription start site) has been inserted between the y wing and body enhancers at position -1868 from the y transcription start site. The w^+mC gene is present downstream of the y coding region. A loxP cassette containing a 1.2kb Fab-7 insulator fragment has been inserted at position -893 relative to the y transcription start site.