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Picornavirales

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Picornavirales
Picornavirus replication cycle
Picornavirus replication cycle
Virus classification e
(unranked): Virus
Realm: Riboviria
Kingdom: Orthornavirae
Phylum: Pisuviricota
Class: Pisoniviricetes
Order: Picornavirales

Picornavirales is an order of viruses with vertebrate, invertebrate, protist and plant hosts. The name has a dual etymology. First, picorna- is an acronym for poliovirus, insensitivity to ether, coxsackievirus, orphan virus, rhinovirus, and ribonucleic acid. Secondly, pico-, meaning extremely small, combines with RNA to describe these very small RNA viruses. The order comprises viruses that historically are referred to as picorna-like viruses.

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.

Taxonomy

Phylogenetic tree of representative viruses from order Picornavirales

The following families are recognized:

External links


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