Sequence analysis and expression of the attachment and fusion proteins of canine distemper virus wild-type strain A75/17

The biological properties of wild-type A75/17 and cell culture-adapted Onde rstepoort canine distemper virus differ markedly. To learn more about the m olecular basis for these differences, we have isolated and sequenced the pr otein-coding regions of the attachment and fusion proteins of wild-type can ine distemper virus strain A75/17. in the attachment protein, a total of 57 amino acid differences were observed between the Onder-stepoort strain and strain A75/17, and these were distributed evenly over the entire protein. Interestingly, the attachment protein of strain A75/17 contained an extensi on of three amino acids at the C terminus. Expression Studies showed that t he attachment protein of strain A75/17 had a higher apparent molecular mass than the attachment protein of the Onderstepoort strain, in both the prese nce and absence of tunicamycin. In the fusion protein, 60 amino acid differ ences were observed between the two strains, of which 44 were clustered in the much smaller F2 portion of the molecule. Significantly, the AUG that ha s been proposed as a translation initiation codon in the Onderstepoort stra in is an AUA codon in strain A75/17. Detailed mutation analyses showed that both the first and second AUGs of strain A75/17 are the major translation initiation sites of the fusion protein. Similar analyses demonstrated that, also in the Onderstepoort strain, the first two AUGs are the translation i nitiation codons which contribute most to the generation of precursor molec ules yielding the mature form of the fusion protein.