Intron of the mouse Hoxa-7 gene contains conserved homeodomain binding sites that can functionas an enhancer element in Drosophila

The 5′ flanking sequences and the intron of the mouse Hoxa-7 gene were searched for regulatory elements that can function in Drosophila. Only the intron is able to activate a lacZ fusion gene in various tissues of Drosophila embryos. This enhancer function requires a cluster of three homeodomain binding sites (HB1-element) that are also found in the introns of other Hox genes as well as in a putative autoregulatory element of Ultrabithorax (Ubx), the Drosophila homolog of Hoxa-7. If a single binding site in the autoregulatory element of fushi tarazu (ftz) is replaced by the HB1-element of Hoxa-7, the expression pattern is altered and newly controlled by the homeotic gene caudal (cad). These data suggest that HB1 is a potential target for different homeodomain proteins of both vertebrates and invertebrates.