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Multi-target Parallel Processing Approach for Gene-to-structure Determination of the Influenza Polymerase PB2 Subunit
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Defective assembly of influenza A virus due to a mutation in the polymerase subunit PA

John F Regan1, Yuying Liang, Tristram G Parslow

  • 1BioMedical Sciences Graduate Program, University of California, San Francisco, California 94143, USA.

Journal of Virology
|December 15, 2005
PubMed

Insights

A novel influenza A virus polymerase mutant (J10) unexpectedly blocked virus assembly and release, despite normal RNA synthesis. This suggests the PA subunit has a critical, previously unknown role in virion formation and packaging.

Area of Science:

  • Virology
  • Molecular Biology
  • Structural Biology

Background:

  • Influenza A virus RNA-dependent RNA polymerase (RdRp) comprises three subunits (PA, PB1, PB2).
  • The RdRp synthesizes viral mRNAs and replicates viral genomic RNA segments (vRNAs) via cRNA intermediates.
  • PA is one of the three essential RdRp subunits, but its precise roles beyond RNA synthesis are not fully understood.

Purpose of the Study:

  • To functionally characterize site-directed mutants of the influenza A virus PA polymerase subunit.
  • To investigate the role of specific PA residues in viral RNA replication and virus assembly.
  • To identify novel functions of the PA subunit in the influenza A virus life cycle.

Main Methods:

  • Site-directed mutagenesis of the influenza A virus PA gene.
  • Analysis of viral RNA expression and replication in mutant viruses.
  • Infectivity assays, including plaque formation and virus assembly assays.
  • Localization studies of mutant PA protein and viral RNA products.

Main Results:

  • 16 PA mutants were generated, most showing quantitative defects in RNA expression and infectivity.
  • A specific mutant (J10), affecting residues 507-508, exhibited minimal RNA synthesis defects but completely abolished plaque formation.
  • J10 polymerase synthesized functional mRNAs and replicated RNA templates, with correct protein and RNA localization.
  • J10 failed to produce infectious virus particles in assembly assays, with reduced genomic RNA in released material.

Conclusions:

  • The PA subunit plays a previously unrecognized role in influenza A virus assembly or release.
  • The J10 mutant highlights a function of PA beyond RNA synthesis, potentially involving virion core structure or vRNA packaging.
  • Further studies are needed to elucidate the precise mechanism by which PA influences influenza virus particle formation.

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