Caprine kappa-casein (CSN3) polymorphism: new developments in molecular knowledge.

A high degree of polymorphism was recently found at the kappa-casein (CSN3) locus in the domesticated goat (Capra hircus). In the present study, 2 new patterns previously identified by PCR-single-strand conformation polymorphism analysis (SSCP) were characterized. The allele provisionally named "X" (GenBank Accession no. AY350425) differs from CSN3C (AF485341) by a (silent) A-->G substitution at position 509 of the goat CSN3 reference sequence (X60763). As this newly identified sequence changes the amino acid sequence, and the already known CSN3C allele (AF485341) has an additional silent mutation, we proposed a change in nomenclature to reflect these changes, indicating the silent mutation with the prime symbol (i.e.,'). The CSN3M allele (provisionally named "Y") results in a new protein variant, differing by 2 nonsynonymous mutations from the CSN3F allele. The new variant is characterized by a G-->A transition at nucleotide position 384, resulting in the amino acid exchange Asp90-->Asn90, and a C-->T transition at position 550, resulting in a Val145-->Ala145 substitution. Thus, the number of alleles identified in the domesticated goat has increased to 16, of which 13 are protein variants and 3 are silent mutations, involving a total of 15 polymorphic sites in CSN3 exon 4. Data on the distribution of the main alleles in 7 goat breeds of Europe, West Africa, and the Near East show differences in the occurrence and frequency of the alleles between breeds and geographic origin with the highest number of alleles found in goat breeds from the Near East.