Genome packaging in influenza virus
Influenza A virus is the prototype of the Orthomyxoviridae, and like all members of this family, the negative-sense RNA that comprises its genome is divided into separate segments. These vRNA segments share a common organisation; a long central coding region (in antisense), sometimes encoding more than one polypeptide, flanked by relatively short untranslated regions (UTRs) and at the termini, sequences conserved between segments that show partial complementarity. The vRNA segments are separately encapsidated into ribonucleoprotein (RNP) structures by viral polypeptides. These RNPs act as independent units for the purposes of viral RNA synthesis, which occurs in the nuclei of infected cells. Replicated vRNAs are exported (as RNPs) from the nucleus via the cellular CRM1 pathway, and at the final stage of viral assembly, are incorporated into the virion as it buds from the apical plasma membrane of the cell. The process of virion assembly is not well understood but is thought to involve a series of protein-protein interactions between the cytoplasmic tails of the viral integral membrane proteins, the matrix protein and the RNPs.
Genome segmentation confers evolutionary advantages on influenza viruses, but also poses a problem in virion assembly. The eight segments encode 12 identified polypeptides. At least one copy of each of the eight vRNAs must be packaged for a single virion to be able to initiate a productive infection. Until recently, the process by which this was achieved was poorly understood, but a clearer picture has begun to emerge of a mechanism for specifically packaging a full genome, mediated by cis-acting packaging signals in the vRNAs. This review aims to summarise the thought processes and experimental evidence leading up to the currently accepted model for influenza A genome packaging and to highlight the main questions remaining.
Genome packaging in influenza A virus. J Gen Virol. Dec 2 2009
Related:
- Animation of influenza replication
- The Biology of Influenza
- Hungry for hosts – gene flow in influenza virus
Tags: Biology, Genetics, genome, Microbiology, packaging, RNA, Science, Virology, virus
