Organization and structure of wild rabbit kappa2 genes: implications for regulation of kappa expression

In domestic populations, the rabbit kappa light chains are known to be encoded by two loci which are unequally expressed. The kappa1 chains account for the majority of total serum kappa chains, and display an unusual complex polymorphism. In order to study the evolution and the putative correlations between the expression, the organization and the structure of the kappa genes, we analysed the kappa loci in wild rabbit populations. The kappa genes of b95, b97 and b98 allotypes are organized in two loci similar to that of domestic rabbits. The structure of the constant region of the kappa2 locus was determined from a wild rabbit which expresses b95 allotype kappa1 chains. The Ckappa2bas2 of b95 displays a single silent mutation when compared to Ckappa2bas2 associated with b4 and one amino acid change relative to Ckappa2bas1 chain. Therefore, in contrast to the kappa1 locus, the constant regions of the kappa2 locus display strong conservation during evolution. A model based on conformation of the kappa chains is discussed to explain the evolution and expression of the two kappa loci.