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

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Abstract
SUMMARY: Using gel electrophoresis a genetic polymorphism of αs2-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 αs2-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 αs2-Cn A at pH 3.0.The sequence of the polypeptide chain αs2-Cn D differs from that of αs2-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 αs2-Cn is closely linked to the cluster αsl-Cn–β-Cn-K-Cn. The 4 casein species are thus synthesized by 4 closely linked loci.