Junctional diversity in Xenopus immunoglobulin light chains.

Xenopus cDNA sequences encoding the homolog of mammalian kappa (kappa) light (L) chains were isolated from isogenic tadpole and adult individuals to investigate whether there existed stage-specific immunoglobulin L chain expression and somatic diversification. In the course of these studies rearrangements to a sixth J(L) gene segment and a pseudogene (J(L)psi) were found, and it is suggested that the order of these gene segments with respect to the L chain constant (C) region exon is: J(L)6-J(L)1-J(L)2-J(L)3-J(L)4-J(L)5-J(L)psi-C(L). The cDNA junctional diversity was analyzed; few N and P regions were found and almost all the CDR3 were 9 codons in length. There were restricted patterns of recombination site resolution, and this is attributed to some constraint in JL coding end processing.