Abstract
Fusion of rubella virus-infected cells was induced by their brief treatment at pH below 6.0. Exposure of rubella virus to pH 5 caused an irreversible conformational change of the viral envelope glycoproteins, E1 and E2. The change was manifested in the marked reduction in both infectivity and haemagglutinating activity of the virus, the increased resistance of E1 and decreased resistance of E2 polypeptides to proteolytic digestion with trypsin, and the acquisition of liposome- binding activity of the virus. The above changes are presumed to mimic the events occurring in the acidic environment within endosomes following endocytosis of the virus.