Picornavirales

Picornavirales is an order of viruses with vertebrate, insect, algal or plant hosts.[1] The name has a dual etymology.[2] First, picorna- is an acronym for poliovirus, insensitivity to ether, coxsackievirus, orphan virus, rhinovirus, and ribonucleic acid.[2] Secondly, pico-, meaning extremely small, combines with RNA to describe these very small RNA viruses.[2]

Picornavirales
Virus classification
(unranked): Virus
Realm: Riboviria
Phylum: incertae sedis
Order: Picornavirales
Families

The families within this order share a number of common features:

  • The virions are non-enveloped, icosahedral, and about 30 nanometers in diameter.
  • The capsid has a "pseudo T=3" structure, and is composed of 60 protomers each made of three similar-sized but nonidentical beta barrels.
  • The genome is made of one or a few single-stranded RNA(s) serving directly as mRNA, without overlapping open reading frames.
  • The genome has a small protein, VPg, covalently attached to its 5' end, and usually a poly-adenylated 3' end.
  • Each genome RNA is translated into polyprotein(s) yielding mature viral proteins through one or several virus-encoded proteinase(s).
  • A hallmark of the Picornavirales is a conserved module of sequence domains, Hel-Pro-Pol, which is typical of (from the amino- to the carboxy-end of the polyprotein):
    • A Helicase belonging to superfamily III
    • [the VPg is encoded between these two domains]
    • A chymotrypsin-like Proteinase where the catalytic residue is typically a cysteine rather than a serine,
    • A polymerase belonging to superfamily I; this conserved module is a hallmark of the Picornavirales

The evolution of picorna-like viruses seems to have antedated the separation of eukaryotes into the extant crown groups.[3]

Taxonomy

The taxonomy of this group has been reorganized by the International Committee on Taxonomy of Viruses in its 9th report in 2011.[4] The order contains six families and two unassigned genera. Although they did show some similarities, the families Caliciviridae and Potyviridae have not been included in the order, because they differed in some key features (capsid symmetry, absence of conservation in the sequence module, etc.).

References
  1. Le Gall, Olivier; Christian, Peter; Fauquet, Claude M.; King, Andrew M. Q.; Knowles, Nick J.; Nakashima, Nobuhiko; Stanway, Glyn; Gorbalenya, Alexander E. (2008-04-01). "Picornavirales, a proposed order of positive-sense single-stranded RNA viruses with a pseudo-T = 3 virion architecture". Archives of Virology. 153 (4): 715–27. doi:10.1007/s00705-008-0041-x. PMID 18293057.
  2. "Picornaviridae" (html). International Committee on Taxonomy of Viruses (ICTV). October 2017. Retrieved 5 February 2019.
  3. Koonin, Eugene V.; Wolf, Yuri I.; Nagasaki, Keizo; Dolja, Valerian V. (2008). "The Big Bang of picorna-like virus evolution antedates the radiation of eukaryotic supergroups". Nature Reviews Microbiology. 6 (12): 925–939. doi:10.1038/nrmicro2030. PMID 18997823.
  4. "Picornavirales - Positive Sense RNA Viruses - Positive Sense RNA Viruses (2011) - International Committee on Taxonomy of Viruses (ICTV)". International Committee on Taxonomy of Viruses (ICTV). Retrieved 2017-04-27.


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