Transgenic construct used to study a chromatin boundary element. Contains a w^+* marker allele, a ftz enhancer, a loxP cassette that includes a 917bp fragment from the 1.6kb intergenic region which separates myo and ey and in which all five BEAF-32 protein binding sites of the the ME boundary element have been mutated (CGATA to CTCGA), an Hsp70 promoter followed by the lacZ coding region and a scs' insulator.