The interaction of proteins encoded by Drosophila homeotic and segmentation genes with specific DNA sequences.

The ANT-C gene cluster is part of a network of genes that govern pattern formation in the development of Drosophila. The ANT-C genes encode proteins that contain a conserved 60 amino acid sequence, the homeodomain. Here we show that the homeodomains encoded by two of the ANT-C loci confer sequence-specific DNA-binding activity. The DNA sequence specificities of the Dfd and ftz homeodomains appear to overlap completely in vitro, indicating that differences in regulatory specificity among ANT-C and BX-C proteins (assuming that differences exist) must be a consequence of the nonconserved protein sequences found outside of the homeodomains. Deletions that remove sequences from either end of the ftz homeodomain abolish DNA-binding activity, consistent with the commonly held assumption that the homeodomain is a structural domain. The relevance of in vitro DNA-binding experiments to the regulatory function of ftz is supported by our finding that a temperature-sensitive ftz mutation that causes a pairwise fusion of embryonic segments also reduces the affinity of the ftz homeodomain for DNA. Restriction fragments containing ftz homeodomain binding sites were identified within a 90 kb stretch of DNA extending the Antp P1 and P2 promoters. Binding sites appear to be clustered near the P1 promoter but also occur near P2 and in the region between the two. The task remains of determining which of these sequences mediate regulation of Antp by ftz or by other genes that encode closely related homeodomains.