Characterisation of Rainbow Trout CDNAs Encoding a Secreted and Membrane-bound Ig Heavy Chain and the Genomic Intron Upstream of the First Constant Exon

Two different rainbow trout cDNA sequences encoding a heavy chain secreted Ig (Hs) and a part of a membrane-bound heavy chain Ig (Hm) are reported. The sequences were most similar to those encoding the Ig heavy chains (IgH) of other teleost fish. As in the Hm of the other teleost fish the rainbow trout Hm results from the splicing of the 3' end of the third constant exon (CH3) to the sequence encoding the membrane-bound domain. Analysis of a rainbow trout IgH genomic clone revealed that a joining heavy chain (JH) segment, different to the one observed in the cDNA, is located 825 bp 5' of the CH1 exon. The sequence also contains possible enhancer-like and octamer-like motifs.