The structural correlates of the rabbit light chain b allotypes: Sequence studies of b5 and b6 chains

Rabbit kappa light chains of allotype b5 and b6 were prepared from antibodies of restricted heterogeneity made by animals hyperimmunized with, respectively, strain III and strain II pneumococcal vaccines. The amino-acid sequence of several tryptic peptides were determined. The variable region fragments of the b5 and b6 chains appear to be quite similar to the corresponding fragments of b4 and b9 chains, albeit some residues seem to be allotype associated. In contrast the chains of different allotypes vary right from the start of the constant region in a number of positions, suggesting that b allotypes correlate with amino-acid substitutions in this region. The number of substitutions between the b5 and b6 and the previously determined b4 and b9 constant regions sequences ranges from 20 to 35%. Serological studies suggest that Leporidae b allotypes diverged no more than 2 × 10⁶ years ago. By this time only 1% of the substitutions could be generated by ‘conventional evolution’. Duplication and mutation of the individual C_K genes could account for the high level of divergence observed. The data reported here support the notion that the structural genes encoding the light chain constant regions of the various b allotypes coexist on the same chromosome and that the allelism is controlled by a regulatory mechanism.