HOX GENES IN EVOLUTION - PROTEIN SURFACES AND PARALOG GROUPS

The clustered Hox genes, which encode homeodomain transcription factor s, control cell fates along the anterior-posterior axis. Differences b etween Hox proteins cause differences between body parts. Vertebrates have 13 Hox subgroups, called paralog groups, which can be correlated with some of the insect and Amphioxus genes, and have remained distinc tive for hundreds of millions of years. We identify characteristic res idues that define the different paralog groups. some paralog groups ca n be recognized by the homeodomain sequence alone; others only by usin g characteristic residues outside the homeodomain. Mapping characteris tic residues onto the known homeodomain crystal structure reveals that most of the homeodomain amino acids that distinguish paralog groups a re oriented away from the DNA, in positions where they might engage in protein-protein interactions.