Transgenic construct used in an analysis of Trithorax response elements (TREs) in the bxd region of Ubx. A 4kb BamHI-KpnI fragment from the bxd/pbx region upstream of Ubx (nucleotides 216,487 to 220,533, coordinates relative to GenBank accession number U31961) is fused in reverse orientation upstream of the w+mC minigene.