A recombinant bacteriophage containing the entire alpha-lactalbumin gene was isolated from a human genomic library constructed in bacteriophage lambda L47. Within this recombinant the 2.5 kb alpha-lactalbumin gene is flanked by about 5 kb of sequence on either side. The complete nucleotide sequence of the gene and its immediate flanking sequences were determined and compared with those of the rat alpha-lactalbumin gene. These studies showed that the size, organization and sequence of the exons have been highly conserved, whereas the introns have diverged considerably. In particular, the first intron of the human gene was found to contain an Alu repetitive sequence not present in the rat. A high degree of homology (67%) was also observed in the 5′ flanking regions, extending as far as 655 nucleotide residues upstream of the transcriptional initiation site. Comparison of the 5′ flanking sequences of these two alpha-lactalbumin genes with those of five casein genes has revealed the presence of a highly conserved region [consensus sequence: RGAAGRAAA(N)TGGACAGAAATCAA(CG)TTTCTA], extending from position -140 to -110 in all seven sequences examined, suggesting a possible regulatory role in the hormonal control or tissue-specific expression of milk protein genes in the mammary gland.

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