Importance of coronavirus negative-strand genomic RNA synthesis prior to subgenomic RNA transcription.
The (-)-strand viral RNAs that result from after infection of cells with coronaviruses, which possess RNA genomes of message polarity, are genomic-sized and subgenomic-sized. Each of the (-)-strand subgenomic RNAs corresponds in size to each of the subgenomic mRNA species that are made in infected cells. We tested whether (-)-strand subgenomic RNAs might initially be synthesized from the input single-stranded (+)-strand genomic RNA prior to the production of subgenomic mRNAs. We used a mouse hepatitis virus (MHV) defective interfering (DI) RNA. from which subgenomic RNA was produced in DI RNA-replicating cells, because this DI RNA had a functional MHV intergenic region inserted in its interior. MHV samples containing the DI particles were irradiated with UV-light and then superinfected into cells that had been infected with MHV 4 h prior to superinfection. Northern blot analysis of intracellular RNAs that were extracted 3 h after superinfection showed that genomic DI RNA and subgenomic DI RNA had similar UV-target sizes, indicating that (-)-strand genomic DI RNA synthesis from input genomic DI RNA probably occurred prior to the subgenomic-size DI RNA synthesis. We discuss why, in the course of coronavirus transcription, (-)-strand genomic-length coronavirus RNA synthesis might occur before subgenomic-sized RNAs of either polarity are made.
Maeda
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Department of Microbiology, and Institute for Cellular and Molecular Biology, The University of Texas at Austin, 78712-1095, USA.
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Makino
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D000818:Animals; D051379:Mice; D006517:Murine hepatitis virus / Q000235:genetics*; D012367:RNA, Viral / Q000096:biosynthesis*; D014158:Transcription, Genetic
D012367:RNA, Viral