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An UItrabithorax Protein Binds Sequences Near Its Own and the Anfennapedia PI Promoters

The homeotic gene Ultrabifhorax (Ubx), located in the bithorax complex of Drosophila, encodes a family of closely related proteins that direct the developmental fates of posterior thoracic and anterior abdominal metameres. We have purified a member of the Ubx protein family from an overproducing E. coli strain and have shown that it is a sequence-specific DNA binding protein. The protein binds tightly to sequences near its own promoter and near the Pl promoter of Anfennapedia (Antp), a homeotic gene Ubx is known to repress from genetic studies. The binding sites occur in clusters downstream of the transcription start sites, and far upstream at Antp Pl. They range in size from 40 to 90 bp, and contain tandem repeats of the trinucleotide TAA or the related hexanucleotide TAATCG. These results suggest that the regulatory activities of Ubx are direct and are mediated by binding of Ubx proteins to promoter region sequences.