THE COMPLETE SEQUENCE OF THE GENE ENCODING BOVINE ALPHA-S2-CASEIN

From a bovine genomic library, five overlapping clones, spanning some 50 kb, have been isolated. These clones contain the complete alphas2-casein-encoding gene (alphas2ca) and its 5' and 3' flanking regions. The nucleotide (nt) sequence of the complete gene including 25 1 0 bp of the 5' flanking region and 276 bp of the 3' region has been determined. The total length of alphas2ca appears to be 18 483 bp and, therefore, it is the longest of the four bovine casein-encoding genes. The alphas2ca gene is comprised of 18 exons ranging in size from 21 to 266 nt. There are 16 Alu-like artiodactyla retroposons inserted at ten different locations within the gene. About 14% of the gene is composed of these repetitive sequences. Although the organization of alphas2ca appears to be similar to that of the alphas1-casein-encoding gene (alphas1ca), sequence comparisons and the length of the exons indicate that it is more closely related to the beta-casein-encoding gene. Furthermore, it is shown that both genes could have evolved from a common ancestor by means of internal duplications.