Biosynthesis of Influenza Virus RNA
Using fowl plague virus as a model highly virulent influenza A virus, we have studied the transcription and replication of the eight segments of the negative-stranded RNA genome. Initiation of transcription requires a 5’ cap-containing RNA primer molecule which is recognised by PB2, the virion polypeptide product of RNA seament 1. During transcription, the 5’ cap plus 10–15 nucleotides are transferred to influenza virus mRNAs, resulting in sequence heterocreneitv at their 5’ termini. Transcription is terminated by polyadenylation at a tract of uridine residues 17–22 nucleotides from the 5’ terminus of each segment of the genome RNA template.
The site of RNA transcription appears to be the cell nucleus. Addition of toyocamycin to infected cells results in accumulation of virus-specific transcripts in the nucleus, and blocks the production of spliced mRNAs normally processed from transcripts of segments 7 and 8. Transcription is strictly regulated during normal replication, resulting in temporal control of polypeptide synthesis. This regulation can be abolished by cycloheximide, indicating that newly synthesised polypeptides (so far undefined) control transcription.
Little is known concerning the synthesis of progeny virion RNAs. Production of template cRNAs involves read-through of the polyadenylated site by an unknown mechanism. Since these cRNAs can be synthesised in the absence of new virion RNA synthesis, it is likely that onlt the input vRNAs are required to act as templates in their production.
KeywordsInfluenza Adenosine Electrophoresis Polypeptide Methionine
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