In a previous study, it was found that the synthesis of hemagglutinating virus of Japan (HVJ; Sendai virus)-specific proteins was inhibited at the transcriptional level at 41° in LLC-MK2 cells. During an investigation of the temperature sensitivity of HVJ production in other host cells, the synthesis of HVJ-specific proteins was recognized even at 41° in Vero cells. Viral production, however, was not detected, indicating the inhibition of steps after the synthesis of viral proteins. Hemadsorption activity was not detected at 41°, suggesting problems with the envelope proteins, especially hemagglutinin-neuraminidase (HN) protein, at the cell membrane. Immunofluorescent staining and surface immunoprecipitation showed that HN protein was not present on the surface in spite of its localization in the cytoplasm. Further, analysis of the cell membrane fraction suggested that fusion (F) protein was integrated into the cell membrane but HN protein was not at 41°. Electron microscopic observation showed that budding sites with spike structures formed and nucleocapsids assembled under the sites at 41° without HN protein, although budded HVJ virions were not detected. At this time, F protein was exposed to the cell membrane and interacted with matrix and nucleocapsid proteins. The results suggested that the suppression of HVJ production at 41° was due to the absence of HN protein in the membrane of Vero cells.

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