Transgenic construct used to study the ability of the CTCF protein to independently form a functional insulator. Contains a y reporter (including the upstream body and wing enhancers and the intronic bristle enhancer) upstream of a mini-w reporter. An FRT cassette containing the UbxPRE has been inserted in between the y body and wing enhancers. Sequence encoding four binding sites for CTCF has been inserted upstream of the y enhancers. A loxP cassette containing four binding sites for CTCF has been inserted between the upstream y enhancers and the y promoter.