Background Paper Transcription and Replication of Coronavirus RNA: A 1989 Update
The genomic RNA of coronaviruses has two unique features. Firstly, it is one of the largest stable RNAs known to exist in nature and is unquestionably the largest viral genomic RNA. The complete sequence of avian infectious bronchitis virus (IBV) RNA shows that its size is 27.6 kilobases (kb) (Boursnell et al., 1987). Although the complete sequences of other Coronavirus genomic RNAs are not yet available, preliminary data from several laboratories indicate that the genomic RNA of mouse hepatitis virus (MHV) is as long as 32 kb (Shieh and Lai, unpublished observations). The large size of these RNAs poses a theoretical quandary for the replication of Coronavirus RNA, considering the high error frequency of RNA-dependent RNA synthesis observed in some systems (Holland et al., 1982; Steinhauer and Holland, 1986). How does Coronavirus RNA replicate faithfully despite the high error frequency of RNA synthesis? It is possible that a proof-reading mechanism operates to correct unavoidable mistakes which are expect d to occur in almost every RNA molecule of this size. Secondly, Coronavirus RNA contains a leader sequence (approximately 72 nucleotides) which is repeated at the 5′-end of every subgenomic mRNA species. This structural organization appears to be similar to that of most of eukaryotic mRNAs which contain leader sequences derived by RNA splicing. Yet the Coronavirus RNA genome does not have consensus splicing signals and the virus replicates exclusively in the cytoplasm (Wilhelmson et al., 1981; Brayton et al., 1981), where there is no conventional RNA splicing machinery. Furthermore, UV transcriptional mapping studies suggest that Coronavirus mRNA species are transcribed independently (Jacobs et al., 1981), instead of being derived by cleavage of a precursor RNA. Thus, a new transcriptional mechanism must operate to transcribe Coronavirus mRNAs.
KeywordsInfectious Bronchitis Virus Mouse Hepatitis Virus Transcriptional Initiation Site Murine Hepatitis Virus Avian Infectious Bronchitis Virus
Unable to display preview. Download preview PDF.
- Boursnell, M. E. G., Brown, T. D. K., Foulds, I. J., Green, P. F., Tomley, F. M., andGoogle Scholar
- Brierley, I., Boursnell, M. E. G., Binns, M. M., Bilimoria, B., Blok, V. C, Brown, T. D. K., and Inglis, S. C., 1987, An efficient ribosomal frame-shifting signal in the polymerase-encoding region of the Coronavirus IBV, EMBOJ., 6:3779.Google Scholar
- Lai, M. M. C., 1986, Coronavirus leader-RNA-primed transcription: an alternative mechanism to RNA splicing, BioEssays. 5:257.Google Scholar
- Soe, L. H., Shieh, C.-K., Baker, S. C., Chang, M.-F., and Lai, M. M. C., 1987,Google Scholar
- Sequence and translation of the murine Coronavirus 5’-end genomic RNA reveals the N-terminal structure of the putative RNA polymerase. J. Virol, 61: 3968–3976.Google Scholar