Regulation by homeoproteins: A comparison of deformed-responsive elements

Homeotic genes of Drosophila melanogaster encode transcription factors that specify segment identity by activating the appropriate set of target genes required to produce segment-specific characteristics. Advances in understa nding target gene selection have been hampered by the lack of genes known t o be directly regulated by the HOM-C proteins. Here we present evidence tha t the gene 1.28 is likely to be a direct target of Deformed in the maxillar y segment. We identified a 664-bp Deformed Response Element (1.28 DRE) that directs maxillary-specific expression of a reporter gene in transgenic emb ryos. The 1.28 DRE contains in vitro binding sites for Deformed and DEAF-1. The Deformed binding sites do not have the consensus sequence for cooperat ive binding with the cofactor Extradenticle, and we do not detect cooperati ve binding to these sites, though we cannot rule out an independent role fo r Extradenticle. Removing the four Deformed binding sites renders the 1.28 DRE inactive in vivo, demonstrating that these sites are necessary for acti vation of this enhancer element, and supporting the proposition that 1.28 i s activated by Deformed. We show that the DEAF-I binding region is not requ ired for enhancer function. Comparisons of the 1.28 DRE with other known De formed-responsive enhancers indicate that there are multiple ways to constr uct Deformed Response Elements.