Structural relationships among genes that control development: sequence homology between the Antennapedia, Ultrabithorax, and fushi tarazu loci of Drosophila.

Genes that regulate the development of the fruit fly Drosophila melanogaster exist as tightly linked clusters in at least two cases. These clusters, the bithorax complex (BX-C) and the Antennapedia complex (ANT-C), both contain multiple homoeotic loci: mutations in each locus cause a transformation of one part of the fly into another. Several repetitive DNA sequences, including at least one transposon, were mapped in the ANT-C. DNA from the 3' exon of Antennapedia (Antp), a homoeotic locus in the ANT-C, hybridized weakly to DNA from the 3' exon of Ultrabithorax (Ubx), a homoeotic locus in the BX-C. DNA from each of these 3' exons also hybridized weakly to DNA from the fushi tarazu locus of the ANT-C. The fushi tarazu (ftz) locus controls the number and differentiation of segments in the developing embryo. Sequence analysis of the cross-hybridizing DNA from the three loci revealed the conservation of predicted amino acid sequences derived from coding parts of the genes. This suggests that two homoeotic loci and a "segment-deficient" locus encode protein products with partially shared structures and that the three loci may be evolutionarily and functionally related.