Hox Gene - Hox Proteins

Hox Proteins

The products of Hox genes are Hox proteins. Hox proteins are transcription factors, which are proteins that are capable of binding to specific nucleotide sequences on the DNA called enhancers where they either activate or repress genes. The same Hox protein can act as a repressor at one gene and an activator at another. For example, in flies (Drosophila melanogaster) the protein product of the Hox gene Antennapedia activates genes that specify the structures of the 2nd thoracic segment, which contains a leg and a wing, and represses genes involved in eye and antenna formation. Thus, legs and wings, but not eyes and antennae, will form wherever the Antennapedia protein is located. The ability of Hox proteins to bind DNA is conferred by a part of the protein referred to as the homeodomain. The homeodomain is a 60 amino acid long DNA-binding domain (encoded by its corresponding 180bp DNA sequence, the homeobox). This amino acid sequence folds into a helix-turn-helix motif that is stabilized by a third helix. The consensus polypeptide chain is (typical intron position noted with dashes):

RRRKRTA-YTRYQLLE-LEKEFLF-NRYLTRRRRIELAHSL-NLTERHIKIWFQN-RRMK-WKKEN