Partial aminoterminal amino acid sequences of chicken major histocompatibility antigens

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Partial amino acid sequences of the aminoterminal regions of mouse H-2 and human HLA major histocompatibility antigens (MHAs) have recently been determined (Capra et al. 1976, Cunningham et al. 1976, Ewenstein et al. 1976, Silver et al. 1976, Appella et al. 1976, Ballou etal . 1976, Bridgen et al. 1976, Terhorst et al. 1976, 1977). The results clearly showed the structural homology of the mouse and human antigens, but presented an unexpected feature: the homology between duplicated genes within a species (e.g., H-2D and H-2K) was greater than any interspecies homology. This result suggests that the gene duplications giving rise to the H-2D and K (and H L A A , B, and C) loci may have taken place late in evolution, after the divergence of mice and humans from a common ancestor (Silver and Hood 1976). Further information about the evolution of the mouse and human major histocompatibility complexes (MHCs) can be gained from studying their homologs in such nonmammalian species as Xenopus (Du Pasquier et al. 1975) and the chicken (Hfila 1977). The chicken B complex and the mammalian MHCs have very similar biological properties, and one class of products of the B complex--the B antigens--are clearly homologous to the mammalian MHAs in their apparent molecular weight (about 40,000) and association with a smaller polypeptide (//2microglobulin) of molecular weight 11,500 (Ziegler and Pink 1975, 1976). Limited amino acid sequence data on the B antigens of one inbred chicken strain (SC: Vitetta et al. 1977) confirm this conclusion. In this paper, we report partial amino acid sequence data from the aminoterminal regions of the B antigens of the inbred WA and WB chicken strains. The B antigens of these two strains have slightly different apparent molecular weights, suggesting that the two strains may differ at only one locus coding for MHAs [since it is unlikely that the products of duplicated loci would evolve in parallel to give different apparent molecular weights in the two strains (Ziegler and Pink 1975, 1976)]. The