Isolation and sequencing of the cDNA encoding the motilin precursor from sheep intestine

The nucleotide sequence of sheep prepromotilin has been determined from cDNA clones. The nucleotide sequence revealed an open reading frame of 345 nucleotides encoding 115 amino acids. The amino acid sequence deduced from the nucleotide sequence consists of a 25 amino acid signal peptide, followed by the 22 amino acid motilin sequence, an endoproteinase cleavage site (Lys23-Lys24) and a 66 amino acid motilin associated peptide (MAP). Compared with human and pig motilin we observed two substitutions at positions 10 (Leu-->Val) and 19 (Asn-->Tyr). The second one may explain the poor cross-reactivity of ovine motilin with C-terminally directed antibodies against porcine motilin. The sheep motilin precursor exhibits the same structure as the motilin precursors from rabbit, pig and man. However, while there is considerable identity in the amino acid sequences as well as in the nucleotide sequences of the signal peptide and motilin, the MAP strongly differs between the species. This may be a result of 'mosaic evolution' at the molecular level.