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Interference by a non-defective variant of influenza A virus is due to enhanced RNA synthesis and assembly
1Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ont., Canada.
Abstract:
Mouse-adapted influenza A virus, FM-MA, interferes with the replication of wild-type strains on co-infection. The interference phenotype was previously mapped to FM-MA segment 2 encoding a mutant PB1 protein, the catalytic component of the RNA polymerase complex. To identify the point at which FM-MA interferes with wild-type A/HK/1/68 (HK), the relative levels of transcription and genome replication of the PB1, NP and M1 genes were determined for FM-MA and HK viruses in co-infected cells using RT-PCR. All stages of HK macromolecular synthesis (primary and secondary transcription, genomic RNA, complementary RNA and protein synthesis) were suppressed relative to FM-MA. Infection with HK virus alone resulted in the accumulation of similar or greater amounts of RNA at late times post-infection relative to FM-MA thus indicating that the presence of FM-MA specifically compromised HK transcription and replication in co-infected cells. However early in infection FM-MA was ten times more active in mRNA transcription than HK or its parental strain FM. FM-MA's ability to interfere was primarily due to an increased capacity for primary transcription. FM-MA genomes were also selectively assembled into progeny virus from cells co-infected with HK and FM-MA, a step which was distinct from the capacity for enhanced RNA synthesis. This suggests that interference of HK growth by FM-MA in mixed infections results from two distinct events: a preferential synthesis of FM-MA-specific macromolecules which is then augmented by a preferential assembly of FM-MA genomes.
Insights
Mouse-adapted influenza A virus (FM-MA) hinders wild-type influenza virus replication by enhancing its own transcription and genome replication. This interference occurs through preferential macromolecular synthesis and progeny virus assembly.
Area of Science:
- Virology
- Molecular Biology
- Genetics
Background:
- Mouse-adapted influenza A virus (FM-MA) inhibits wild-type influenza strains during co-infection.
- This interference is linked to a mutation in the PB1 protein (segment 2) of FM-MA, a key component of the viral RNA polymerase.
- Understanding the precise mechanism of interference is crucial for controlling influenza virus spread.
Purpose of the Study:
- To pinpoint the stage at which FM-MA interferes with the replication of wild-type A/HK/1/68 (HK) influenza virus.
- To compare the transcription and replication efficiencies of FM-MA and HK viruses in co-infected cells.
Main Methods:
- Quantitative reverse transcription polymerase chain reaction (RT-PCR) was used to measure the relative levels of transcription and genome replication for PB1, NP, and M1 genes.
- Comparative analysis of macromolecular synthesis (RNA and protein) at different stages of infection in single and co-infected cells.
Main Results:
- FM-MA significantly suppressed all stages of HK macromolecular synthesis (transcription, genome replication, protein synthesis) compared to FM-MA alone.
- Early in infection, FM-MA exhibited a tenfold higher mRNA transcription activity than HK or its parent strain (FM).
- FM-MA's interference capability stemmed from enhanced primary transcription and selective assembly of its own genomes into progeny viruses.
Conclusions:
- FM-MA interferes with wild-type influenza virus replication through two distinct mechanisms: enhanced synthesis of its own macromolecules and preferential assembly into new virions.
- The mutant PB1 protein in FM-MA plays a critical role in its superior transcription and replication capabilities.
- These findings provide insights into viral interference and potential targets for antiviral strategies.