Chicken IgA H chains. Implications concerning the evolution of H chain genes.
A cDNA clone (A1) encoding for a novel chicken Ig H chain isotype was isolated. In sequence comparison to mammalian H chains, A1 C region was most closely related to the alpha isotype. For example, identities of 35%, 32%, and 31% at the amino acid level to rabbit C alpha, C mu, and C gamma were observed, respectively. Distribution of the glucosamine acceptor sites (Asn-X-Ser/Thr) in A1 C region was typical of alpha H chains. Moreover, A1 C region probe hybridized to a 2.2-kb RNA species expressed in the epithelial lymphoid tissues. Thus, A1 was identified as the avian homologue for mammalian alpha H chains. Interestingly, the chicken C alpha was structurally consistent with four complete CH domains, whereas only three domains are present in the mammalian C alpha genes. In addition, interdomain sequence alignments suggested that the homologue for the chicken C alpha 2 domain is missing from the mammalian alpha H chains. Thus, the present data suggest evolution of the IgA isotype before the segregation of avian and mammalian species. Also, the first C alpha gene may have consisted of four CH domains, whereas reorganization of the C alpha 2 region led to the generation of hinge region in the mammalian alpha H chains.
Mansikka
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Department of Medical Microbiology, Turku University, Finland.
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D002645:Chickens / Q000235:genetics*; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D005796:Genes; D005803:Genes, Immunoglobulin; D006801:Humans; D007127:Immunoglobulin Constant Regions / Q000235:genetics; D007137:Immunoglobulin alpha-Chains / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D016415:Sequence Alignment
D007127:Immunoglobulin Constant Regions; D007137:Immunoglobulin alpha-Chains; D004247:DNA