Focusing on the goat casein complex

The analysis of casein polymorphisms in goat species is rather difficult, because of a large number of muta- tions at each locus, and the tight linkage involving the 4 casein genes. Three goat breeds from Northern Italy, Orobica, Verzasca, and Frisa, were analyzed at the ca- sein complex by milk isoelectrofocusing and analyses at the DNA level to identify the majority of all known polymorphisms. The casein gene structure of the 3 local breeds at αS1-casein (CSN1S1), β-casein (CSN2), αS2- casein (CSN1S2), and κ-casein (CSN3) was compared with that of Camosciata, a more widely distributed breed. A new allele was identified and characterized at CSN2 gene, which seemed to be specific to the Frisa breed. It was named CSN2*E, and was characterized by a transversion TCT→TAT responsible for the amino acid exchange Ser166→Tyr166 in the mature protein. The casein haplotype structure is highly different among breeds. A total of 26 haplotypes showed a frequency higher than 0.01 in at least 1 of the 4 breeds considered, with 12, 3, 5, and 19 haplotypes in Frisa, Orobica, Verzasca, and Camosciata breeds, respectively. Only 13 haplotypes occurred at a frequency higher than 0.05 in at least 1 breed. With the molecular knowledge of each locus, the ancestral haplotype coding for CSN1S1*B, CSN2*A, CSN1S2*A, and CSN3*B protein variants can be postulated. A protein evolutionary model consid- ering the whole casein haplotype is proposed.