Antennapedia Homeodomain

The antennapedia homeodomain is a sequence-specific transcription factor from the organism Drosophila melanogaster. This protein is encoded by the Antennapedia (antp) gene. However, the antennapedia homeodomain (Antp) shown here is a mutant. Cys39 has been changed to a Serine residue (C39-->S). Antp is a member of a regulatory system that gives cells specific positions on the anterior-posterior axis of the organism. Thus, Antp aids in the control of cell development in the mesothorax segment in Drosophila.
The homeobox domain, or homeodomain, is one that binds DNA through a helix-turn-helix structural motif. Proteins that contain a homeobox domain usually play a role in development, and many of these are sequence-specific transcription factors such as Antp.
The antennapedia homeodomain is 68 amino acid residues long. It contains four alpha helices: Helix 1 (res.10-21)=Red, helix 2 (res.28-38)=Yellow, helix 3 (res.42-52)=Green, and helix 4 (res.53-59)=Blue. Helices 2 and 3 adopt a helix-turn-helix motif from residues 28 to 52. This motif is similar to those found in prokaryotic repressor proteins.

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