''Picornavirales'' is an order of viruses with vertebrate, invertebrate,

protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exclu ...

and plant hosts. The name has a dual etymology. First, ''picorna-'' is an

acronym An acronym is a word or name formed from the initial components of a longer name or phrase. Acronyms are usually formed from the initial letters of words, as in ''NATO'' (''North Atlantic Treaty Organization''), but sometimes use syllables, as ...

for poliovirus, insensitivity to

ether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again b ...

, coxsackievirus, orphan virus, rhinovirus, and ribonucleic acid. Secondly,

pico- A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or submultiple of the unit. All metric prefixes used today are decadic. Each prefix has a unique symbol that is prepended to any unit symbol. The pr ...

, 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 barrel In protein structures, a beta barrel is a beta sheet composed of tandem repeats that twists and coils to form a closed toroidal structure in which the first strand is bonded to the last strand (hydrogen bond). Beta-strands in many beta-barrels are ...

s. * 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 VPg (viral protein genome-linked) is a protein that is covalently attached to the 5′ end of positive strand viral RNA and acts as a primer during RNA synthesis in a variety of virus families including Picornaviridae, Potyviridae and Caliciv ...

covalently A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...

attached to its

5' end Directionality, in molecular biology and biochemistry, is the end-to-end chemical orientation of a single strand of nucleic acid. In a single strand of DNA or RNA, the chemical convention of naming carbon atoms in the nucleotide pentose-sugar-r ...

, and usually a poly-adenylated

3' end Directionality, in molecular biology and biochemistry, is the end-to-end chemical orientation of a single strand of nucleic acid. In a single strand of DNA or RNA, the chemical convention of naming carbon atoms in the nucleotide pentose-sugar-ri ...

. * Each genome RNA is translated into

polyprotein Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called proteases ...

(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 ** he 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 A polymerase is an enzyme ( EC 2.7.7.6/7/19/48/49) that synthesizes long chains of polymers or nucleic acids. DNA polymerase and RNA polymerase are used to assemble DNA and RNA molecules, respectively, by copying a DNA template strand using bas ...

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

The following families are recognized: *''

Caliciviridae The ''Caliciviridae'' are a family of "small round structured" viruses, members of Class IV of the Baltimore scheme. Caliciviridae bear resemblance to enlarged picornavirus and was formerly a separate genus within the picornaviridae. They are p ...

'' *''

Dicistroviridae ''Dicistroviridae'' is a family of viruses in the order '' Picornavirales''. Invertebrates, including aphids, leafhoppers, flies, bees, ants, and silkworms, serve as natural hosts. There are 15 species in this family, assigned to three genera ...

'' *''

Iflaviridae ''Iflaviridae'' is a family of positive sense RNA viruses insect-infecting viruses. Some of the insects commonly infected by iflaviruses include aphids, leafhoppers, flies, bees, ants, silkworms and wasps. The name "Ifla" is derived from the ...

'' *''

Marnaviridae ''Marnaviridae'' is a family of positive-stranded RNA viruses in the order ''Picornavirales''. The first species of this family that was isolated is ''Heterosigma akashiwo RNA virus'' (HaRNAV) in the genus '' Marnavirus'', that infects the tox ...

'' *''

Picornaviridae Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are viruses that represent a large family of small, positive-sense, single-stranded RNA viruses with a 30 nm i ...

'' *'' Polycipiviridae'' *'' Secoviridae'' *'' Solinviviridae''

References

External links

ICTV's last release of virus taxonomyUniProt Taxonomy
{{Taxonbar, from=Q6553 Animal virology Virus orders Riboviria