RNA-dependent RNA Polymerase Activity in Murine Coronavirus-infected Cells

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Abstract
The multiplication of murine coronavirus strains A59 or JHM in mouse Sac(-) cells was unaffected by the presence of .alpha.-amanitin at concentrations which inhibited the host cell DNA-dependent RNA polymerase activity. In cells infected with the A59 virus strain, actinomycin D-resistant RNA synthesis could readily be detected by pulse-labeling with [3H]uridine; this virus-specific RNA synthesis was not induced in the presence of the protein synthesis inhibitor anisomycin. A new RNA-dependent RNA polymerase activity was detected in the late particle fraction of A59 virus-infected cells. Optimal conditions for enzyme activity in vitro were established. Maximum activity occurred 5 h after infection, coincident with the peak of virus-specific RNA synthesis detected by pulse-labeling in vivo.