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Nat Rev Microbiol. 2008 Apr;6(4):315-9. doi: 10.1038/nrmicro1858. Epub 2008 Mar 3.

Redefining viruses: lessons from Mimivirus.

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Unité des Rickettsies, IRD-CNRS UMR 6236, IFR-48, Faculté de Médecine, 27 Bd Jean Moulin, 13385 Marseille, France.


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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