Viruses can explore the limits of genome minimalism by exploiting other viruses. For example, satellite viruses rely on the polymerase of a helper virus for replication. Zhang et al. describe a capsidless single-stranded RNA (ssRNA) virus, yado-kari virus 1 (YkV1), that is trans-encapsidated by a co-infecting double-stranded RNA (dsRNA) virus, yado-nushi virus 1 (YnV1). YkV1 has a single protein, an RNA-dependent RNA polymerase (RdRp), whereas YnV1 has both an RdRp and a capsid protein. Although the YkV1−YnV1 interaction shares similarities with helper−satellite systems and the other known example of trans-encapsidation, it represents a novel lifestyle in important respects: YkV1 and YnV1 have different genome types; replication occurs inside the trans-capsid; and the interaction is cooperative, as YkV1 boosts YnV1 production. The authors speculate that YkV1 is an evolutionary intermediate destined to become an independent dsRNA or ssRNA virus.
References
Zhang, R. et al. A capsidless ssRNA virus hosted by an unrelated dsRNA virus. Nat. Microbiol. http://dx.doi.org/nmicrobiol.2015.1 (2016)
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Attar, N. Two viruses, one capsid. Nat Rev Microbiol 14, 65 (2016). https://doi.org/10.1038/nrmicro.2016.4
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DOI: https://doi.org/10.1038/nrmicro.2016.4