Although Hox proteins have fundamental roles in development, researchers have long been puzzled by what creates their binding specificity. Now, Walter Gehring and co-workers add a piece to that puzzle (see ). The Hox DNA-binding homeodomain has low sequence specificity, and co-factors are thought to contribute to this specificity by binding to a conserved YPWM motif(found in most Hox proteins). Gehring's lab previously demonstrated that ectopic expression of the Drosophila Hox gene Antennapedia(Antp) causes cells of the eye to adopt the developmental fate of the wing. Now they show that YPWM is required for this eye-to-wing transformation and, using a yeast two-hybrid system, have identified a YPWM-binding protein called BIP2. Using gain-of-function experiments and a new bip2 mutant allele, the authors show that the ANTP-BIP2 interaction is required for the ectopic formation of wing structures. BIP2 is a TATA-binding protein associated factor (TAF), making this the first demonstration of a link between a Hox protein and the basal transcription machinery.
