The structure and evolution of immunoglobulin kappa chain constant region genes in the genus Rattus

We have cloned and sequenced the C-kappa (Ck) genes from seven species and subspecies of rats which have diverged over the past few million years in Australia. Comparisons of these sequences with each other and the Ck genes of the laboratory rat, Rattus norvegicus, indicate noncoding regions have accumulated fewer mutations than adjacent coding sequences, and amino acid replacing nucleotide substitutions in the coding regions have accumulated at a rate at least as great as silent changes. Exactly the opposite of both of these findings is observed when comparisons are made between Ck or other genes from more distantly related species, indicating that these features may be characteristic of Ck short-term evolutionary gene divergence. Changes in the coding regions of these genes result in a non-random distribution of amino acid substitutions on the three-dimensional alpha-carbon backbone of the Ck domain in the most serologically distinct forms of Ck. While phylogenetic relationships inferred from the Ck nucleotide sequences are in general agreement with those derived from other data, considerable differences are seen in rates of accumulation of Ck gene nucleotide substitutions vs rates of accumulation of enzyme polymorphisms.