New genetic polymorphisms within ovine - and S2-caseins

Casein genes in ruminants are organized in a cluster including S1-casein (CSN1S1), -casein (CSN2), S2-casein (CSN1S2), and -casein (CSN3). Considering the results obtained in cattle and goat species concerning the influence of genetic polymorphisms on milk composition, quality, and technological properties, research on the polymorphisms of ewe’s milk has known a new impulse in the last decade. A total of 54 samples belonging to the Massese dairy breed, to the double pourpose (milk and meat) Garfagnina population and to the Pomarancina and Zerasca meat populations, reared in the Centre of Italy, were analysed by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP). New PCR-SSCP patterns were found in both CSN2 and CSN1S2 genes. Sequencing of the samples carrying the new patterns revealed 2 new variants at CSN2 gene. Frequencies of the 2 variants in the samples analysed were 0.18 and 0.02. The less common variant is characterized by a silent mutation in the triplet coding for Gln192, whereas in the more frequent one a C to A transversion is responsible for the aminoacid exchange Leu196→Ile196. At the CSN1S2 gene only a new variant was found with a frequency of 0.02. The variant is characterized by two linked mutations: a C to G transversion, responsible for the aminoacid change Asn200→Lys200 already described at the protein level, and a T to A transversion at the 14th nucleotide of the 16th intron. The ovine caseins deserve a bigger attention that has to be directed to a complete characterization of the described variants and to the understanding of their functional meaning.