Molecular cloning and evolution of transferrin cDNAs in salmonids

Transferrin complementary DNAs were cloned from the livers of seven species in three genera of salmonids (kokanee salmon Oncorhynchus nerka, amago salmon Oncorhynchus masou ishikawa, masu salmon Oncorhynchus masou masou, Japanese char Salvelinus pluvius, brook trout Salvelinus fontinalis, lake trout Salvelinus namaycush, and brown trout Salmo trutta) subsequent to polymerase chain reaction amplification with primers derived from conserved regions of transferrin cDNA sequences. The transferrin cDNAs of the seven species of salmonids had sizes of 2.2 to 2.4 kb and encoded an open reading frame consisting of 691 amino acids with a putative signal peptide of 18 amino acids. The alignment of salmonid transferrin cDNAs showed a duplicated structure and conserved anion-binding residues, iron-binding residues, and cysteine residues for disulfide bridges. The deduced amino acid sequences of the seven salmonid transferrin cDNAs share 85% to 99% homology. A phylogenetic tree of amino acid sequences of transferrin cDNAs from salmonids showed that the relationship among the three genera of salmonids (Oncorhynchus, Salvelinus, and Salmo) is well correlated with that derived from classic morphologic and genetic analyses.