Sequence of C region of L chains from Xenopus laevis Ig.

A cDNA expression library, prepared from Xenopus laevis splenocytes, was screened with antibodies to Xenopus Ig. One clone, lambda XIg23, reacted with antibodies to IgY and to IgM; the insert hybridized to approximately 1.3-kb RNA from spleen, the approximate size expected for L chain mRNA. An additional clone, lambda XIg31, was identified by cross-hybridization. The inserts of lambda XIg23 and lambda XIg31 begin in the third framework region of the V region and extend through the C region to the poly(A) tail. Except for a single nucleotide difference, the two C region sequences are identical. The amino acid sequence of the C region was compared with the sequences of a variety of C kappa and C lambda, as well as to C region sequences of L chains from Rana catesbeiana and from two species of shark. The Xenopus C region resembles mouse and human C kappa slightly more than C lambda. The similarity of the Xenopus and Rana C regions to each other is approximately the same as that of either amphibian sequence to mammalian CL. The data are discussed in terms of the evolution of kappa and lambda C regions.