Focusing on the goat casein gene complex

The analysis of casein polymorphisms in goat species
is rather difficult, because of a large number of mutations
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 casein
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 alphaS1-casein (CSN1S1), beta-casein (CSN2), alphas2-casein (CSN1S2), and kappa-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 considering
the whole casein haplotype is proposed.