A cluster type organization of the loci of the immunoglobulin light chain in Atlantic cod (Gadus morhua L.) and rainbow trout (Oncorhynchus mykiss Walbaum) indicated by nucleotide sequences of cDNAs and hybridization analysis.

Antibody screening and colony hybridization of cDNA libraries have been used to isolate clones of the immunoglobulin light (IgL) chain from Atlantic cod (Gadus morhua L.) and rainbow trout (Oncorhynchus mykiss Walbaum). Sequence analysis shows dissimilarities in the constant part of the molecule (CL) within each species. Comparisons of the amino acid sequences of the constant parts of the IgL chains show a 55% identity between the two teleost species. When compared with other species the highest similarities are found to the constant domain of the IgL chain from mammals (30%-37%), but the teleost IgL chain can be classified neither as kappa nor lambda. The VL domain in Atlantic cod and rainbow trout is also more similar to those of mammals than to those of other animal species, but no difference between kappa and lambda was noticed. Genomic Southern blots hybridized with fragments coding for the constant part of IgL gave several bands larger than 2 kilobases and a similar pattern was obtained with fragments coding for the variable part. These results show that the locus of the IgL chain has a multiple organization in teleost fish and that the locus has an organization similar to that of sharks. Several of the cDNA clones isolated from both the head kidney and the spleen represent nonrearranged or nonspliced mRNA, and northern blot analysis shows that such transcripts are present in both the head kidney and the spleen.