Phylogenetic relationships of HMG box DNA-binding domains.

HMG boxes were initially identified as DNA-binding domains of the human RNA polymerase I (pol I) transcription factor hUBF and the animal high-mobility-group (HMG) protein family HMG1. Since then, numerous sequences of HMG-box-containing HMG proteins and other DNA-binding proteins from several species have become available. By sequence comparisons of a selected range of HMG boxes from these proteins and the construction of phylogenetic trees we show that the HMG box is highly conserved between DNA-binding proteins of organisms from all three eukaryotic kingdoms and that HMG boxes are linked by distinct evolutionary relationships. In addition, most HMG boxes display comparable hydropathy profiles and amino acid arrangements, which could serve as nuclear targeting sequences.