Abstract :
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.
