Rooted phylogenetic tree of the human ORs. The tree was generated by ClustalX program using 347 hOR protein sequences with the human melanocortin-4 receptor sequence as a root. Fragments starting from the conserved amino-terminal N-glycosylation site and ending 12 residues downstream of predicted TM7 were used for phylogenetic analysis. The numbers indicate the bootstrap value from 1,000 replicates. The bar corresponds to the graphical distance equivalent to 10% sequence divergence. OR names in parentheses correspond to HORDE analogs of the OR sequences identified by us. This figure is available as an additional data file in PDF format.