Leucine at position 383 of fusion protein is responsible for fusogenicity of wild-type mumps virus in B95a cells.

OBJECTIVE Mumps virus is isolated in Vero cells and, recently, B95a cells have been reported to be susceptible to it. Currently circulating wild-type mumps virus strains (genotypes B, G, J and L) induced cytopathic effects in both Vero and B95a cells. On the other hand, the Hoshino vaccine strain (KO3) did not induce cytopathic effects in B95a cells. In this study, differences in fusion inducibility were investigated. METHODS Nucleotide sequences of the fusion (F) and hemagglutinin-neuraminidase (HN) protein regions were compared. The F and HN expression plasmids were constructed and fusion analysis was conducted, using recombinant F expression plasmids under the control of T7 RNA polymerase. RESULTS Extensive cell fusion was observed when B95a cells were transfected with the wild-type F expression plasmid as the F expression partner; 13-16 amino acid differences were observed in the F protein region between the KO3 and the wild types. F expression plasmids with leucine at position 383 of the F protein induced large cell fusion in B95a cells. CONCLUSION Leucine at position 383 of the F protein of the wild types was the critical amino acid for fusion inducibility in B95a cells.