Immunoglobulin allotypes of rabbit kappa chains: polymorphism of a control mechanism regulating closely linked duplicated genes?

The amino acid sequence of the constant (CK) region from the kappa immunoglobulin chains of a b9 rabbit is compared with the CK sequences, taken from the literature, of a b4 rabbit. These CK regions differ by 33% of their amino acid sequences and by three sequence insertions or deletions (sequence gaps). These extensive differences together with other published observations suggest that the b9 and b4 CK genes may not be simple alleles, but rather they may be encoded by closely linked CK genes present in every rabbit whose expression is regulated by a polymorphic control mechanism.