Characterization of a C alpha gene of swine.

The cDNA sequence encoding the constant region of the porcine IgA heavy chain as well as the exon-intron structure of the germline gene, have been determined. A cDNA clone (1A1) spanning the CH3 domain and part of the CH2 domain was isolated from a porcine mesenteric lymph node cDNA library. Clone 1A1 was aligned with a PCR-generated DNA fragment encompassing the CH1 domain through the 5' end of the CH3 domain to derive the complete cDNA sequence. Comparison with other mammalian C alpha heavy chains (hinge regions excluded) indicated that the deduced amino acid sequence of porcine C alpha is most homologous with the human C alpha subclasses (> 70%), followed by mouse C alpha (61%) and a consensus sequence of the 13 rabbit C alpha heavy chains (59%). The greatest sequence homology was found among the CH3 domains in all species. A striking feature of porcine C alpha is its short six amino acid hinge which like other mammalian IgAs, is encoded with the CH2 domain. Sequence analysis of germline C alpha, generated by PCR from liver or sperm DNA, revealed an exon-intron organization similar to other mammalian C alpha genes. Genomic Southern blot data are consistent with the presence of a single C alpha gene within the porcine genome. Data obtained in these studies will be valuable in pursuing the use of swine as a model in immunological research.