Characterization of equine cDNA sequences for (alpha)S1-, (beta)- and (kappa)-casein

Here we report the entire cDNA sequences for equine (alpha)S1-, (beta)- and (kappa)-casein. Based on interspecies comparison, nine exons were found in equine (beta)-casein and five in (kappa)-casein. In equine (alpha)S1-casein cDNA the exon 5 was missing, which resulted in the total of 18 exons instead of 19 theoretically possible exons in (alpha)S1-casein cDNA. Comparison of DNA sequences representing exon 5 in other species with corresponding equine genomic region confirmed the presence of cryptic exon in horse genomic DNA. Equine (alpha)S1-casein mRNA was present in three forms in the lactating mammary gland and we showed that the two shorter forms were produced by skipping either the exon 8 or exon 15. In horse, as in some other mammals, (beta)- and (kappa)casein are considerably more conserved (sequence identity 53% to 59% and 57% to 67%, respectively) than (alpha)S1-casein which appears as the most variable casein among species (sequence identity 40% to 54%). Interestingly, horse caseins resemble human much more than bovine caseins which may also explain the high dietetic value of maresʹ milk.