EXON SKIPPING IN THE OVINE ALPHA(S1)-CASEIN GENE

The reported cDNA sequences for the bovine (Bos taurus) and ovine (Ovi s aries) alpha(sl)-caseins display a high degree of identity with the exception that a 24 bp region, corresponding to bovine exon 16, is abs ent in the ovine sequence. Here we show that the ovine gene for alpha( sl)-casein contains a sequence block displaying 23/24 identity to bovi ne exon 16, indicating that the absence of this block from ovine mRNA is due not to genomic deletion but to exon skipping. Analysis of the p roducts obtained by reverse transcription of ovine alpha(sl)-casein mR NA followed by amplification, demonstrated the presence of mRNA specie s containing the exon 16 sequence as well as the species in which it h ad been spliced out. It was estimated that the latter constitutes 20% of the total ovine alpha(sl)-casein mRNA. We propose that a substituti on within the donor splice site is responsible for the partial skippin g of exon 16, possibly through the formation of an inhibitory RNA seco ndary structure.