Sequence of caprine alpha s1-casein and characterization of those of its genetic variants which are synthesized at a high level, alpha s1-CnA, B and C.

Abstract

The sequence of caprine alpha s1-casein (199 residues) was established. The peptide chain has the same length as, and shows a 88% degree of identity with, its bovine counterpart. With the ovine alpha s1-casein, the sequence of which was deduced from that of its mRNA, the degree of identity is 97%, counting as one difference a deletion of eight residues in the ovine protein. The differences between the three genetic variants associated with a high alpha s1-casein content in milk are simple substitutions. Variant alpha s1-CnA differs from variant alpha s1-CnB by two substitutions, 16 Leu (A)----Pro (B) and 77 Gln (A)----Glu (B), the latter inducing the appearance of a phosphate group on 75 Ser. Variant alpha s1-CnC differs from alpha s1-CnB by three substitutions, 8 His (B)----Ile (C), 100 Arg (B)----Lys (C) and 195 Thr (B)----Ala (C). The original type of caprine alpha s1-casein could be another hypothetical genetic variant, having the same electrophoretic mobility as alpha s1-CnB.