The nucleotide sequence and deduced amino acid composition of the haemagglutinin and fusion proteins of the morbillivirus phocid distemper virus.

The amino acid composition of the two surface proteins of the recently isolated morbillivirus phocid distemper virus (PDV) were deduced from the nucleotide sequence. The fusion (F) protein of PDV exhibited characteristics similar to those of other morbillivirus F proteins. The overall amino acid similarity with its closest homologue, canine distemper virus (CDV), was 72%. From the context of the starting codons and the requirement for a hydrophobic signal peptide, it is likely that translation of the PDV F mRNA starts at the third AUG, corresponding to codon 95 in the long open reading frame of the PDV F gene. After removal of the signal peptide, F0 starts at amino acid 105. From this position the F protein of PDV and CDV exhibit 84% amino acid similarity. The PDV haemagglutinin (H) protein showed 74% amino acid similarity with CDV H protein and highly conserved features responsible for the tertiary structure. Despite these similarities, the two H proteins show marked antigenic differences when probed with monoclonal antibodies. Earlier studies have indicated that rinderpest virus (RPV) is the prototype virus of the morbillivirus genus, from which first CDV/PDV and later measles virus (MV) evolved. From the close relationship shown in this study, it is likely that the divergence of CDV and PDV occurred after MV evolved from RPV.