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Subviral agents are infectious entities that resemble viruses but lack one or more viral components, such as a capsid or essential replication machinery. These agents include viroids, prions, and satellites, each possessing distinct structural and functional characteristics that influence their mode of infection and replication.Viroids are the simplest subviral agents, consisting of circular, single-stranded RNA molecules without a protein coat. They exclusively infect plants, relying entirely...
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A classification system for virophages and satellite viruses.

Mart Krupovic1, Jens H Kuhn2, Matthias G Fischer3

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Satellite viruses and virophages, often called sub-viral agents, should be classified as true viruses. This study proposes new genera and families for these fascinating viral entities.

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Area of Science:

  • Virology
  • Virus Classification
  • Molecular Biology

Background:

  • Satellite viruses possess structural proteins for virion formation but require helper viruses for replication.
  • Satellite viruses and virophages (infecting protists) are often misclassified as sub-viral agents.
  • Current classification systems do not adequately accommodate satellite viruses.

Purpose of the Study:

  • To establish clear criteria for classifying satellite viruses and virophages.
  • To propose a revised taxonomic framework for these viral entities.
  • To ensure accurate and consistent classification within the viral hierarchy.

Main Methods:

  • Analysis of genetic and structural characteristics of satellite viruses and virophages.
  • Comparative genomics to identify defining viral features.
  • Phylogenetic analysis to inform taxonomic proposals.

Main Results:

  • Defined possession of a coat-protein-encoding gene and virion formation as key criteria for viral classification.
  • Proposed four new genera (Albetovirus, Aumaivirus, Papanivirus, Virtovirus) for plant-infecting (+)RNA satellite viruses.
  • Proposed the family Sarthroviridae (including genus Macronovirus) for arthropod-infecting (+)RNA satellite viruses and the family Lavidaviridae (genera Sputnikvirus, Mavirus) for DNA virophages.

Conclusions:

  • Satellite viruses and virophages meet the criteria for bona fide viruses and warrant formal classification.
  • The proposed taxonomic framework provides a consistent system for classifying these viruses.
  • This classification will enhance our understanding of viral diversity and evolution.