An allele associated with a non dectable amount of as2 casein in goat milk

The goat CSN1S2 locus is characterized by the presence of three alleles, A, B and C, all associated with about 2.5 g/l of protein per allele. The SDS±PAGE analysis of 441 individual milk samples obtained from goats belonging to a population reared in Southern Italy showed that the milk produced by three goats did not apparently contain as2-casein, whereas milk produced by 37 goats showed a less intense electrophoretic band of this casein fraction (about 50%). These results can be explained by hypothesizing the presence of another allele at this locus, CSN1S20, associated with a `null' content of as2-casein. Southern blot, PCR and PCR±RFLP analyses of the DNA region containing the CSN1S2 gene of individuals producing milk with and without as2-casein did not show differences between the two groups. As a consequence, goats producing milk without as2-casein carry an apparently intact gene. The ®rst results obtained by sequencing part of the CSN1S20 allele revealed a G®A transition at nucleotide 80 of the 11th exon which creates a stop codon and could be responsible for the absence of the as2-casein in goat milk. This mutation eliminates a NcoI restriction site. A test based on this polymorphism has been established in order to identify carriers of the CSN1S20 allele.