A genetic and biochemical analysis of a polymorphism of bovine αs2-casein

Abstract

SUMMARY: Using gel electrophoresis a genetic polymorphism of α_s2-casein (Cn) was discovered in individual milk samples from 2 bovine breeds of the eastern part of France (Vosgienne and Montbéliarde). The 3 observed phenotypes (Plate 1) are determined by 2 co-dominant alleles at an autosomal locus. The α_s2-Cn A variant was the only one known up to now in European breeds (reference variant) and ±_s2-Cn D is a new variant, whose bands overlap the β-casein A band at pH 8.6, and migrate faster than α_s2-Cn A at pH 3.0.The sequence of the polypeptide chain α_s2-Cn D differs from that of α_s2-Cn A by the deletion of a very acidic nonapeptide, which includes a cluster of 3 phosphoseryl residues. Due to the characteristics of the reference sequence, this deletion cannot be exactly located but it involves residues 50–58, or 51–59, or 52–60.A genetic analysis shows that locus α_s2-Cn is closely linked to the cluster α_sl-Cn–β-Cn-K-Cn. The 4 casein species are thus synthesized by 4 closely linked loci.