RESUMO
Genetic polymorphisms in CSN3 gene in Pag (Croatia), Sarda (Italy) and Pramenka (Serbia) sheep breeds were investigated. A single nucleotide polymorphism (SNP) was localized by sequence analysis (sequence submitted to GenBank under accession AY237637) relying on an original primer pair. Primers for sequencing (kappa-casF and kappa-casR) were designed on the available CSN3 sequences to amplify the genomic region encoding the major part of the mature protein (exon 4). An SNP was detected at position 237 of the sheep kappa-casein mRNA (reference sequence: GenBank X51822), where a thymine was substituted for a cytosine. The SNP was typed by conventional PCR and SYBR Green I-based real-time PCR. C and T alleles were discriminated using a dedicated set of primers that consisted of one common forward primer (SNP-TC) and two reverse primers (SNP-T and SNP-C), the latter two differing in the 3' end base and in the presence of a 12 bp poly-G tail in SNP-C. The SNP was found in both the heterozygous and the homozygous state in Sarda and Pramenka breeds, and in the heterozygous state only in the Pag breed. The observed allelic frequencies of the SNP were 0.12 in Pag, 0.27 in Sarda and 0.45 in Pramenka.
