(A) Deduced amino acid alignment of XNC and SNC α3 domains with X. laevis and X. tropicalis MHC class Ia. A consensus sequence is shown at the top and dots indicate amino acids identical to this sequence; (-) represent gaps in the alignment and conserved cysteines are in bold and underlined. The MHC class I CD8 binding site is boxed and indicated in bold. (B) The neighbor-joining tree was constructed from amino acid alignments of the alpha 3 domains using pairwise gap deletions and the p-distance method to estimate evolutionary distance. The tree was drawn using MEGA 5.2. and confidence values were measured using 10,000 bootstrap replications with the values indicated at key nodes with * indicating values <50. Species abbreviations are: Xl, X. laevis, St, S. tropicalis; Hs, human; Mm, mouse; Ss, pig; Gg, chicken; Me, tammar wallaby; Wd, short-tailed opossum, Oa, sheep; Ec, horse; Cs, rhinoceros; Dn, nine-banded armadillo; Rp,northern leopard frog and Amcr, Galapagos marine iguana.