Transgenic construct used in a study of the Fab-7 element. Contains two divergently transcribed reporters: a w+C marker and a lacZ reporter driven by a minimal eve promoter. A 200bp SpeI-BamHI enhancer fragment that directs expression of the h stripe 1 (H1) and 1kb spacer (MAR region of the mouse μ light chain gene) have been inserted between the two divergent promoters. A 1kb SalI IAB5 enhancer fragment from the iab-5 cis regulatory region of Abd-B has been inserted downstream of the lacZ reporter.