STRUCTURE OF THE BOVINE LACTOFERRIN-ENCODING GENE AND ITS PROMOTER

Lactoferrin (Lf), a ferric ion (Fe3+)-binding glycoprotein, is found m ost notably in milk, probably to mediate protection against microbial infection of the mammary gland. Based on an initial isolation and sequ encing of a complete cDNA of the bovine Lf gene (bLf), the complete ge ne was obtained from genomic libraries on five overlapping phage lambd a EMBL3 clones. A detailed restriction map and the complete exon/intro n structure of the gene are presented, together with 1 kb of sequence data of the promoter upstream from the proximal exon. The coding seque nce is dispersed over 17 exons spanning 34.5 kb of genomic DNA. While the exons are of similar size, as in other members of the transferrin gene family (Tf), some of the intron sizes are very different. Evoluti onary conservation of both exon sizes and their contribution to the va rious domains of the protein molecule add to the evidence that Lf orig inated via an internal sequence duplication. The promoter sequence lac ks some of the sequence motifs for transcriptional enhancers found in the promoters of human and mouse Lf, suggesting a potential reason for the relatively weak expression of bLf.