Homeodomain (Hox) Transcription Factors
Members of this transcription factor family are characterized by the presence of a homeodomain, which is a 60 amino acid helix-turn-helix DNA-binding domain. The DNA sequence that encodes the homeodomain is called the "homeobox" and homeobox-containing genes are known as "hox genes." The homeodomain is very highly conserved and consists of three helical regions folded into a tight globular structure that binds a 5'-TAAT-3' core motif. The recognition helix within the homeodomain binds the DNA major groove while the amino-terminal tail contacts the DNA minor groove. Interestingly, the homeodomain is also important for nucleocytoplasmic trafficking of hox transcription factors. Members of the hox transcription factor family can function as monomers or homodimers to directly drive transcription of target genes. The major function of hox transcription factors is to pattern the embryonic anterior-posterior body axis. More specifically, hox gene expression is crucial for normal temporospatial limb and organ development.