COMPLETE SEQUENCE-ANALYSIS OF RAT TRANSFERRIN AND EXPRESSION OF TRANSFERRIN BUT NOT LACTOFERRIN IN THE DIGESTIVE GLANDS

Rat milk and digestive juices contain transferrin but not lactoferrin, which is a major iron-binding protein in these secretions of human an d mouse. To compare the structure of rat transferrin to that of transf errins and lactoferrins in other species, we isolated a cDNA clone con taining the entire coding region of transferrin from rat liver and det ermined its sequence. The amino-acid. sequence of rat transferrin had 69.8% identity with that of human transferrin and 48.8% identity with that of human lactoferrin. Rat transferrin, like other transferrins, h ad the potential N-linked glycosylation site only in the C-terminal do main, although lactoferrins characterized so far contained the glycosy lation sites in both the N- and C-terminal domains. Southern and North ern analyses showed that there was the gene specifically hybridized wi th the mouse lactoferrin cDNA in rat genomic DNA, but only the transfe rrin mRNA was detected in mammary gland, submaxillary gland and pancre as oi rat. These results suggest that the rat lactoferrin gene is sile nt in the mammary gland, and transferrin can serve as a functional sub stitute for lactoferrin in rat.