Abstract
Segmentation in Drosophila melanogaster is controlled by a network of interacting genes, many of which encode a homeodomain that confers sequence-specific binding to DNA. One of these, fushi tarazu (ftz), is a transcription factor that regulates a number of segmentation and homeotic genes, including Antennapedia (Antp). To determine the DNA binding specificity of the ftz homeodomain, we performed DNase I footprint analysis on ftz protein binding sites located near the two Antp promoters using a beta-galactosidase/ftz fusion protein synthesized in E. coli. A consensus sequence for the fusion protein's preferred binding site was derived from 19 sites. The consensus sequence contains an ATTA motif, as do the reported consensus sequences for the engrailed (en), even-skipped (eve), and bicoid (bcd) Drosophila homeodomain proteins. We propose DNA bending as an explanation for the presence of a shared motif between proteins with divergent recognition helices: according to this model, bases in ATTA would not directly contact amino acid side chains of the recognition helix but rather would be necessary for bending of the DNA around the homeodomain, perhaps facilitating important protein-DNA contacts.
