“…The second route, which appears to be employed by several other enveloped viruses, is endocytosis of the particle into the cell, after which the viral genome is liberated into the cytoplasm (Dales, 1973;Longberg-Holm & Philipson, 1974). Recently, it has been convincingly shown that several enveloped viruses (White et al, 1980(White et al, , 1983Matlin et al, 1981Matlin et al, , 1982Yoshimura et al, 1982) can fuse efficiently with different target membranes at acidic, but not neutral pH and it has been proposed that fusion is involved in the infectious entry process of enveloped viruses, whereby viral genetic material is liberated into the cytosol either at the plasma membrane or from acidic endosomal compartments (Marsh, 1984).T. KIMURA, S. W. GOLLINS AND J. S. PORTERFIELD Sigma).…”