A Alignment of the amino acid sequences of IDOs restricted to the stretch of amino acids containing the YxxM motif (where x is any amino acid). Residues are highlighted based on increasing conservation level of symbols in the multiple alignment (light gray ≥ 44.4%; dark grey ≥ 66.6%; black ≥ 88.8%). IDOs, homologues of IDO1. Proto-IDOs, homologues of IDO2. Accession number for each specific gene is indicated. 