F1 polypeptides of two canine distemper virus strains: variation in the conserved N-terminal hydrophobic region.

The fusion protein of canine distemper virus was isolated by immunoadsorption from two virus strains, the rapidly growing Onderstepoort strain (forming large plaques) and the Convac vaccine strain (forming microplaques). The F1 subunits of the two fusion proteins were purified by preparative polyacrylamide gel electrophoresis. Direct amino acid sequence analysis revealed that 36-residue N-terminal regions of the proteins from the two strains are identical except at position 9, where Ala in the Convac strain is substituted by Val in the Onderstepoort strain. The two sequences show high homology with the previously determined N-terminal sequence of the F1 polypeptide of measles virus, and moderate homology with corresponding sequences of five paramyxoviruses, emphasizing the occurrence of an extensive conservation of these structures.