ROTAVIRUS-INDUCED FUSION FROM WITHOUT IN TISSUE-CULTURE CELLS

We present the first evidence of fusion from without induced in tissue culture cells by a nonenveloped virus. Electron micrographs of two st rains of rotavirus, bovine rotavirus C486 and rhesus rotavirus, show t hat virally mediated cell-cell fusion occurs within 1 this fusion, inc luding the formation of pores or channels between adjacent fused cells . These data support direct membrane penetration as a possible route o f infection. Moreover, the assay should be useful in determining the m echanisms of cell entry by rotavirus. postinfection. Trypsin activatio n is necessary for rotavirus to mediate cell-cell fusion. The extent o f fusion is relative to the amount of virus used, and maximum fusion o ccurs between pHs 6.5 and 7.5. Fusion does not require virus-induced p rotein synthesis, as virus from both an empty capsid preparation and f rom an EDTA-treated preparation, which is noninfectious, can induce fu sion. Incubation of rotavirus with neutralizing and nonneutralizing mo noclonal antibodies before addition to cells indicates that viral prot ein 4 (VP4; in the form of VP5 and VP8*) and VP7 are involved in fusi on. Light and electron micrographs document of this fusion, including the formation of pores or channels between adjacent fused cells. These data support direct membrane penetration as a possible route of infec tion. Moreover, the assay should be useful in determining the mechanis ms of cell entry by rotavirus.