Abstract

Segmentation of viral genomes allows exchange of intact genes between related viruses when they coinfect the same cell (Fig 1). This exchange is a type of recombination called reassortment. Classical recombination involves the joining of nucleic acid sequences derived from two different templates into one chimeric product. During reassortment, however, entire gene segments are swapped to give rise to chimeric genomes. In both cases, novel genotypes are formed, giving the potential for viruses to evolve. As with genetic change through mutation, most reassortment events yield progeny viruses that are less fit than either parent (Fig 2). Occasionally, however, reassortment gives rise to a combination of genes particularly well suited to a given set of selection pressures, and increased fitness results. Open in a separate window Fig 1 Reassortment requires viruses to meet on multiple scales. For reassortment to occur between viruses of two distinct genotypes, these viruses must infect the same host (A) and the same tissue within that host (B). Either the inoculating viruses or their progeny must come together within the same cell (C). Finally, the coinfecting viral genomes must mix within the coinfected cell, and replicated segments must be copackaged, processes which may be limited by compartmentalization of viral replication and selectivity of genome incorporation, respectively (D). When all of these criteria are met, progeny viruses of both reassortant and parental viral genotypes will emerge from the cell (E).

Highlights

  • Segmentation of viral genomes allows exchange of intact genes between related viruses when they coinfect the same cell (Fig 1)

  • The efficiency of reassortment within a coinfected cell depends on (i) the extent to which viral replication is compartmentalized within the cell and (ii) the stringency of genome packaging and compatibility of packaging signals between coinfecting viruses. The first of these factors determines the level of mixing between coinfecting viral genomes, while the second dictates whether or not segments derived from differing parental strains can be coincorporated into nascent virus particles

  • Incorporation of viral genomes into virions is typically directed by specific nucleic acid sequences, viral protein motifs, or a combination of both

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Summary

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University of Michigan Medical School, UNITED STATES. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Introduction
Physical barriers to reassortment within the cell
Fitness barriers to reassortment
Emergence of novel viruses through reassortment
Conclusions

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