An aminoterminally extended P1-protamine variant in the boar.

We have found a minor form of boar sperm P1-protamine with a six amino acid long N-terminal extension. When this sequence was compared with the recently published gene sequence of boar P1-protamine, and with DNA sequences obtained from the boars studied here, a perfect match was found with the 5'-region upstream of the ATG initiation codon of the authentic P1-protamine. Since no extra in-frame ATG initiation codons are present in the 5'-region of the gene, we conclude that the translation of boar P1-protamine variant starts with a non-AUG initiation codon, CUG, which precedes the codon of the first amino acid (serine) of the sequenced variant.