OCCURRENCE OF A LINE SEQUENCE IN THE 3' UTR OF THE GOAT ALPHA(S1)-CASEIN E-ENCODING ALLELE ASSOCIATED WITH REDUCED PROTEIN-SYNTHESIS LEVEL

The E allele of the alpha(s1)-casein (alpha(s1)-Cas)-encoding gene is associated with a reduced casein content in milk. Structural analysis of mRNA and sequencing of amplified genomic DNA fragments, have reveal ed that this allele contains a 457-bp insertion within exon 19 (last u ntranslated exon). This insert is a truncated long interspersed repeat ed element (LINE) containing part of the ORF-2, the 3' UTR and the pol y(A) tail of the original retroposon. This LINE sequence was found to be highly repeated in the goat genome. The threefold reduction in the amount of alpha(s1)-CasE mRNA in the total, as well as in the polysoma l fractions, as compared with its A counterpart, leads one to suppose either a reduced transcriptional rate of allele E or/and a decreased s tability of the relevant mRNA. Northern blot and PCR experiments sugge sted the setting up of highly stable secondary structures involving th e 3' UTR of the alpha(s1)-CasE transcript. The mRNA folding calculatio ns support such an hypothesis, by base-pairing interactions between th e E allele messenger poly(A) tail and a long poly(U)-stretch occurring at the 5' end of the insertion. In addition, since A + U-rich motifs are also present in the truncated LINE insertion, we propose that this extra sequence might be responsible for the lower milk alpha(s1)-Cas content by reducing the allele E mRNA stability.