Partial amino acid sequences of kappa-chains of rat immunoglobulins: genetic and evolutionary implications

Partial amino acid sequences have been determined for several kappa-type light chains prepared from sera or urine of inbred LOU/C/Wsl rats bearing plasma cell tumors. Comparison of these sequences with those of human, rabbit, and mouse kappa-chains available in the literature indicates that the constant region of rat kappa-chains shows more amino acid sequence homology to that of the mouse kappa-chain than to human and rabbit kappa-chains, a result expected from the phylogenetic relationship of the species compared. Examination of the N-terminal amino acid sequences indicated that the variable regions of rat kappa-chains can also be classified into subgroups according to degree of sequence homology in a manner similar to that done for kappa-chains of other species (e.g., human, rabbit, and mouse). However, the prototype amino acid sequences of kappa-chain variable region subgroups of the rat were not homologous to those of other species including the closely related mouse. The implications of this observation with respect to the genetics and evolution of immunoglobulins are discussed.