Characterization of a Small Plaque Mutant of the A59 Strain of Mouse Hepatitis Virus Defective in Cell Fusion
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The virions of murine coronaviruses contain nucleocapsid protein and two membrane associated proteins E1 and E2. E2 or S glycoprotein forms the peplomer or spike protein and, as shown by Lawrence Sturman and Kathryn Holmes and co-workers (Sturman et al., 1985), is synthesized initially as a 180,000 Dalton glycoprotein that is cleaved into two 90,000 Dalton glycoproteins. They have also demonstrated that the cleaved form of E2 is required for cell fusion (Sturman et al., 1985) and that there are host-dependent differences in the proteolytic cleavage of E2 and in cell fusion (Frana et al., 1985). Recently, Stuart Siddell (Siddell, 1986) has sequenced the E2 gene of the JHM strain of mouse hepatitis virus (MHV) and found a protease cleavage site (arg-arg-ser) approximately in the middle of the open reading frame of RNA 3, the messenger RNA encoding E2.