Transgenic construct used to study a potential chromatin boundary element in an enhancer blocker assay. Contains a w^+* marker allele, a ftz enhancer, a loxP cassette that includes a 2227bp fragment from the intergenic region between ey and bt (including the 8th exon and 3'UTR of ey), an Hsp70 promoter followed by the lacZ coding region and a scs' insulator.