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Redefining viruses: lessons from Mimivirus

Abstract

Viruses are the most abundant living entities and probably had a major role in the evolution of life, but are still defined using negative criteria. Here, we propose to divide biological entities into two groups of organisms: ribosome-encoding organisms, which include eukaryotic, archaeal and bacterial organisms, and capsid-encoding organisms, which include viruses. Other replicons (for example, plasmids and viroids) can be termed 'orphan replicons'. Based on this suggested classification system, we propose a new definition for a virus — a capsid-encoding organism that is composed of proteins and nucleic acids, self-assembles in a nucleocapsid and uses a ribosome-encoding organism for the completion of its life cycle.

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Figure 1: Mimivirus infecting Acanthamoeba polyphaga.
Figure 2: Clusters of orthologous groups (COGs) in Mimivirus and traditional cellular organisms.
Figure 3: Capsid proteins from viruses that infect organisms from all three domains of life.
Figure 4: Redefining viruses.

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Acknowledgements

The authors thank A. Hecker and P.E. Fournier for help with the figures.

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Correspondence to Didier Raoult.

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DATABASES

Entrez Genome

PBCV1

PRD1

STIV

TMV

Entrez Genome Project

Candidatus Carsonella ruddii

Encephalitozoon cuniculi

Escherichia coli

Gemmata obscuriglobus

Mycoplasma mycoides

Nanoarchaeum equitans

Sulfolobus solfataricus P2

FURTHER INFORMATION

Didier Raoult's homepage

Chambers Reference Online

NCBI COG s database

Oxford English Dictionary Online

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Raoult, D., Forterre, P. Redefining viruses: lessons from Mimivirus. Nat Rev Microbiol 6, 315–319 (2008). https://doi.org/10.1038/nrmicro1858

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