INTRON OF THE MOUSE HOXA-7 GENE CONTAINS CONSERVED HOMEODOMAIN BINDING-SITES THAT CAN FUNCTION AS 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. Onl y the intron is able to activate a lacZ fusion gene in various tissues of Drosophila embryos. This enhancer function requires a cluster of t hree homeodomain binding sites (HB1-element) that are also found in th e introns of other Hox genes as well as in a putative autoregulatory e lement of Ultrabithorax (Ubx), the Drosophila homolog of Hoxa-7 If a s ingle binding site in the autoregulatory element of fushi tarazu (ftz) is replaced by the HB1-element of Hoxa-7, the expression pattern is a ltered and newly controlled by the homeotic gene caudal (cad). These d ata suggest that HB1 is a potential target for different homeodomain p roteins of both vertebrates and invertebrates.