Pathogenic murine coronaviruses I. Characterization of biological behavior in vitro and virus-specific intracellular RNA of strongly neurotropic JHMV and weakly neurotropic A59V viruses

JHM virus (JHMV) and A59 virus (A59V) are neurotropic members of the hepatoencephalitis group of murine coronaviridae. JHMV has a markedly greater neurotropism for weanling BALB/c mice than does A59V. Both viruses display one-hit kinetics when grown in vitro in 17CL-16 cells, a clone of BALB/c3T3 cells. Virus-specific intranuclear, cytoplasmic, and surface antigens have been observed for both viruses by immunofluorescence. The intranuclear antigen appears first at about 2 hr after infection (hpi) followed by the development of the cytoplasmic and surface antigens at 3 hpi at 38.5°. Most, if not all cells that develop the intranuclear antigen, produce cytoplasmic antigen and presumably progeny virus. Progeny virus production is independent of cell fusion and formation of syncytia. Virus-specific ribonucleoprotein is synthesized in the presence of 1 μg/ml actinomycin D, a concentration sufficient to inhibit the synthesis of cellular ribonucleoprotein species that have sedimentation properties similar to the virus-specific species. The virus-specific ribonucleoprotein species that is resistant to 10 mM EDTA, presumptive virion ribonucleoprotein, has a sedimentation value in sucrose of about 230 S for JHMV and 200 S for A59V. The species of virus-specific ribonucleoprotein that are sensitive to 10 mM EDTA presumptive messenger ribonucleoprotein, are about 40–100 S in sucrose for both viruses. The purified presumptive virion RNA is about 50 S in sucrose for both viruses. The major species of presumptive mRNA of both viruses is about 18 S with secondary species of about 28 S in sucrose. Denaturation of the virus-specific RNA with heat and dimethylsulfoxide does not appreciably alter the sedimentation profiles of either the presumptive virion RNA or mRNA species.