Characterization and genetic study of the ovine α S2 -casein (CSN1S2) Allele B

An interesting and quite complex protein pat- tern has been described at ovine milk proteins but the genetic control of the variation observed was assessed only in few cases. The aim of this work was to characterize the ovine as2-casein (CSN1S2) B variant, first observed in the Italian Gentile di Puglia, a fine-wooled ovine breed, and to investigate its occurrence in two further breeds, the Sarda and Camosciata, which are the most widespread dairy breeds in Italy. The B variant differs from the most common form A with two amino acid exchanges: Asp75-Tyr75 and Ile105-Val105. The first substitution, resulting in a loss of a negative charge, is responsible for the higher isoelectric point of the B protein variant, which allows its detection by isoelectric focusing electrophoresis (IEF). The occurrence of CSN1S2*B in Sarda and Comisana was demonstrated. Since the Asp75-Tyr75 substitution modifies the protein electric charge, milk properties may result affected to some extent.