Genomics and proteomics of deleted ovine CSN1S1∗I

Ovine αs1-casein (CSN1S1) allele I (CSN1S1∗I) was characterized at the molecular genetic and protein level. Sequencing of CSN1S1 cDNA and mature protein showed the absence of exon 7 from CSN1S1∗I in comparison with the C″ genetic variant of the C phenotype. This allelic aberration is correlated with a sequence difference in 5′-splice donor sequence of intron 7 (g.656T > A), leading to upstream skipping of exon 7. Consequently mRNA sequence of ovine CSN1S1∗I is 24 bp shorter than complete coding sequence leading to an abbreviation of eight amino acids in the mature protein, resulting in a lower degree of phosphorylation in comparison with CSN1S1∗C″. However CSN1S1∗I was expressed at a quantitative level similar to that for the C″ reference variant. Using amplified created restriction site polymerase chain reaction, a DNA-based test for identification of CSN1S1∗I was developed. Altogether six nucleotide substitutions were identified within intron 6 and intron 7 of CSN1S1 variants, forming three different haplotypes.