NUCLEOTIDE-SEQUENCE OF TRANSFERRIN CDNAS AND TISSUE-SPECIFIC EXPRESSION OF THE TRANSFERRIN GENE IN ATLANTIC COD (GADUS-MORHUA)

Atlantic cod (Gadus morhua) transferrin cDNAs were isolated from a liv er cDNA library using a cod transferrin-derived polymerase chain react ion produce as a hybridization probe. The composite nucleotide sequenc e oi two overlapping clones was 2223 bp in length excluding the poly(A ) sequence and was equivalent to 87% of the 3' end of the Atlantic sal mon transferrin cDNA sequence. Comparison of the deduced amino, acid s equence of cod, salmon, Xenopus and several mammalian transferrins rev ealed that the two fish sequences are more similar with respect to the ir amino acid sequence and the position of additions/deletions than to other vertebrate transferrins. Conservation of the iron-binding domai ns and cysteine residues involved in disulphide bridges indicates that all transferrins share similar tertiary structure and support the hyp othesis that extant vertebrate transferrin genes were derived from a g ene duplication before the divergence of fish, frogs and mammals. Cod transferrin mRNA was detected in both brain and liver RNA and to a muc h lesser extent in RNA isolated from kidney and heart in contrast to s almon and several other vertebrates in which the transferrin gene is n ot expressed in brain.