Characterization of four constant region genes of rabbit immunoglobulin-λ chains

A cDNA plasmid insert encoding the constant (C) region of a rabbit immunoglobulin-λ light chain was used as a probe for screening a rabbit liver genomic DNA cosmid library. This allowed the isolation and identification of four distinct C(λ) genes, designated C(λ1), C(λ2), C(λ3), and C(λ4), which were shown to be widely separated from each other along chromosomal DNA. Their nucleotide sequences have been determined. No in-frame termination codons were found within the coding regions. The C(λ1), C(λ2), and C(λ3) sequences are quite similar to each other, but share less homology with the C(λ4) gene or the cDNA-C(λ) sequence used as a probe. The C(λ) gene coding for the cDNA sequence was not isolated. Translation of the C(λ1), C(λ2), and C(λ3) sequences predicts a Cys-Pro carboxy-terminal amino acid sequence, as found so far only for horse λ-chains. Compared to the other rabbit C(λ) genes, the C(λ3) sequence exhibits two deletions, one of 9 bp, the other of 3 bp. The latter occurs at the same position as in the mouse C(λ2) and C(λ3) genes. These two deletions are located in the loops between anti-parallel β-pleated sheets of the C(λ) domain. When the C(λ) nucleotide sequences from man, mouse, and rabbit are compared, there is less divergence within the same species than for interspecies comparisons. Possible genetic implications of this finding are discussed.