Unexpected beta sub(2)-microglobulin sequence diversity in individual rainbow trout

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 93; no. 7; pp. 2779 - 2784
• Main Authors: Shum, B P, Azumi, K, Zhang, Siwei, Kehrer, SR, Raison, R L, Detrich, H W, Parham, P
• Format: Journal Article
• Language: English
• Published: 01.01.1996
• Subjects: Freshwater; Oncorhynchus mykiss
• ISSN: 0027-8424

For mammals beta sub(2)-microglobulin ( beta sub(2)m), the light chain of major histocompatibility complex (MHC) class I molecules, is invariant (or highly conserved) and is encoded by a single gene unlinked to the MHC. We find that beta sub(2)m of a salmonid fish, the rainbow trout (Oncorhynchus mykiss), does not conform to the mammalian paradigm. Ten of 12 randomly selected beta sub(2)m cDNA clones from an individual fish have different nucleotide sequences. A complex restriction fragment length polymorphism pattern is observed with rainbow trout, suggesting multiple beta sub(2)m genes in the genome, in excess of the two genes expected from the ancestral salmonid tetraploidy. Additional duplication and diversification of the beta sub(2)m genes might have occurred subsequently. Variation in the beta sub(2)m cDNA sequences is mainly at sites that do not perturb the structure of the mature beta sub(2)m protein, showing that the observed diversity of the trout beta sub(2)m genes is not primarily a result of pathogen selection.