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
Electronmicrograph of Foot-and-mouth disease virus
Structure of the Cowpea mosaic virus
Virus classification
(unranked): Virus
Realm: Riboviria
Kingdom: Orthornavirae
Phylum: Pisuviricota
Class: Pisoniviricetes
Order: Picornavirales

Characteristics

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 protease 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
Phylogenetic tree of representative viruses from order Picornavirales

The following families are recognized:[4]

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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". 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. "Virus Taxonomy: 2019 Release". talk.ictvonline.org. International Committee on Taxonomy of Viruses. Retrieved 30 April 2020.
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