Transgenic construct used to study the mechanism of chromosomal boundary action. Contains two divergently transcribed reporters: a mini-w marker plus a lacZ reporter in which two ftz enhancers (UPS, upstream and NE, neurogenic) are fused upstream of Hsp70-lacZ. A 800bp fragment of the Abd-B Fab-8 element has been inserted in between the mini-w marker and the ftz enhancers. A 1.7kb Abd-B Fab-7 blocking fragment has been inserted in between the ftz enhancers and the Hsp70-lacZ reporter. A scs' fragment is present downstream of the lacZ reporter.