Coronavirus Cell-Associated RNA-Dependent RNA Polymerase
Infectious, single-stranded, nonsegmented, polyadenylated, genomic RNA has been demonstrated for the avian infectious bronchitis virus (Lomniczi and Kennedy, 1977; Schochetman et al., 1977), the mouse hepatitis virus (Lai and Stohlman, 1978; Wege et al., 1978), and the transmissible gastroenteritis virus (TGEV) of swine (Brian et al., 1980), three members of the coronavirus family. These properties alone would characterize these coronaviruses as positive-strand viruses and place them in category IV of the Baltimore Scheme (Baltimore, 1971). By analogy with the picornaviruses and togaviruses that have been characterized, also belonging to category IV of the Baltimore scheme, one would not expect to find an RNA-dependent RNA polymerase as part of the virion, but would expect to find such an enzyme in infected cells. In this paper we report that we are unable to detect an RNA-dependent RNA polymerase in purified virions, but we do find it associated with apparent membrane structures in infected cells between 4 and 6 h postinfection, a time when the rate of viral RNA synthesis is maximal. The [3H]UMP-incorporating activity probably represents coronaviral- specified RNA-dependent RNA polymerase since (a) the activity was 10- to 100-fold greater than any similar activity in uninfected cells, (b) the activity was insensitive to actinomycin D, (c) the product was destroyed by RNase but not by DNase, (d) the activity was associated with an apparent replication complex that had sedimentation properties the same as cytoplasmic structures containing virus-specific RNA.
KeywordsApparent Molecular Weight Uninfected Cell Infectious Bronchitis Virus Mouse Hepatitis Virus Transmissible Gastroenteritis Virus
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