The allotypic patchwork pattern of the rabbit IGKC1 allele b5wf: genic exchange or common ancestry?

The protein sequences of different alleles of the rabbit immunoglobulin IGK C1 gene can differ at more than 40% of the amino acid positions. This excep tional degree of allelic divergence raises questions concerning the causal underlying mechanisms. We report the DNA sequence of the coding region of a n allotype which is associated with the mitochondrial lineage A (Southweste rn Spain). At the serological level, this b5wf allotype presents a patchwor k of antigenic determinants which in domestic breeds are characteristic of the b4, b5, and b6 allotypes. The inferred protein sequence of the b5wf all otype was found to differ from that of the b4, b5, and b6 allotypes at 25, 10, and 15% of the amino acid positions, respectively. Sequence comparisons show that the b4-specific epitopes of the b5wf allotype are probably due t o a shared ThrThrGlnThr motif at Kabat positions 153-156. Similarly, the sh ared b5-specific determinants should relate to the motifs 161ThrSerLys163 a nd/or 182LysSerAspGlu185. A monoclonal antibody binding epitope shared amon g the b5wf, b5, and b6 sequences appeared to be correlated with the presenc e of Asp190. Although there is evidence of interallelic genic exchange, seq uence comparisons suggest that the apparent mosaic structure of the b5wf al lotype is better explained by common ancestry and point mutation.