Identification and characterization of cell lines with a defect in a post-adsorption stage of Sendai virus-mediated membrane fusion

In the early stage of infection, Sendai virus delivers its genome into the cytoplasm by fusing the viral envelope with the cell membrane. Although the adsorption of virus particles to cell surface receptors has been character ized in detail, the ensuing complex process that leads to the fusion betwee n the lipid bilayers remains mostly obscure. In the present study, we ident ified and characterized cell lines with a defect in the Sendai virus-mediat ed membrane fusion, using fusion-mediated delivery of fragment A of diphthe ria toxin as an index. These cells, persistently infected with the temperat ure-sensitive variant Sendai virus, had primary viral receptors indistingui shable in number and affinity from those of parental susceptible cells. How ever, they proved to be thoroughly defective in the Sendai virus-mediated m embrane fusion. We also found that viral HN protein expressed in the defect ive cells was responsible for the interference with membrane fusion. These results suggested the presence of a previously uncharacterized, HN-dependen t intermediate stage in the Sendai virus-mediated membrane fusion.