Picornaviridae
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Picornaviruses are a group of related
nonenveloped A viral envelope is the outermost layer of many types of viruses. It protects the genetic material in their life cycle when traveling between host cells. Not all viruses have envelopes. Numerous human pathogenic viruses in circulation are encase ...
RNA virus An RNA virus is a virusother than a retrovirusthat has ribonucleic acid (RNA) as its genetic material. The nucleic acid is usually single-stranded RNA ( ssRNA) but it may be double-stranded (dsRNA). Notable human diseases caused by RNA viruses ...
es which infect
vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s including
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
,
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s, and
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s. They are
virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's 1 ...
es that represent a large family of small, positive-sense, single-stranded RNA viruses with a 30 nm
icosahedral In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes and . The plural can be either "icosahedra" () or "icosahedrons". There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrica ...
capsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may ...
. The viruses in this family can cause a range of diseases including the
common cold The common cold or the cold is a viral infectious disease of the upper respiratory tract that primarily affects the respiratory mucosa of the nose, throat, sinuses, and larynx. Signs and symptoms may appear fewer than two days after exposu ...
,
polio Poliomyelitis, commonly shortened to polio, is an infectious disease caused by the poliovirus. Approximately 70% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe s ...
myelitis,
meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, headache, and neck stiffness. Other symptoms include confusion or ...
,
hepatitis Hepatitis is inflammation of the liver tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes (jaundice), poor appetite, vomiting, tiredness, abdominal pa ...
, and paralysis. Picornaviruses constitute the
family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
''Picornaviridae'', 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 realm '' Riboviria''. There are 158 species in this family, assigned to 68 genera. Notable examples are genera ''
Enterovirus ''Enterovirus'' is a genus of positive-sense single-stranded RNA viruses associated with several human and mammalian diseases. Enteroviruses are named by their transmission-route through the intestine ('enteric' meaning intestinal). Serologic ...
'' (including ''
Rhinovirus The rhinovirus (from the grc, ῥίς, rhis "nose", , romanized: "of the nose", and the la, vīrus) is the most common viral infectious agent in humans and is the predominant cause of the common cold. Rhinovirus infection proliferates in tem ...
'' and ''
Poliovirus A poliovirus, the causative agent of polio (also known as poliomyelitis), is a serotype of the species ''Enterovirus C'', in the family of ''Picornaviridae''. There are three poliovirus serotypes: types 1, 2, and 3. Poliovirus is composed of an ...
''), ''
Aphthovirus ''Aphthovirus'' (from the Greek -, vesicles in the mouth) is a viral genus of the family ''Picornaviridae''. Aphthoviruses infect split-hooved animals, and include the causative agent of foot-and-mouth disease, ''Foot-and-mouth disease virus'' ...
'', ''
Cardiovirus Cardiovirus are a group of viruses within order '' Picornavirales'', family ''Picornaviridae''. Vertebrates serve as natural hosts for these viruses. Taxonomy There are currently six species in the genus: * ''Cardiovirus A'' * '' Cardiovirus B' ...
'', and ''
Hepatovirus ''Hepatovirus'' is a genus of viruses. The genus has nine species, including ''Hepatovirus A'', which is the causative agent of hepatitis A. Taxonomy These species are recognized: * ''Hepatovirus A Hepatitis A is an infectious disease of the ...
''.


Etymology

The name "picornavirus" has a dual
etymology Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the Phonological chan ...
. Firstly, the name derives from ''picorna''- which 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 "''p''oliovirus, ''i''nsensitivity 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 be c ...
, ''c''oxsackievirus, ''o''rphan virus, ''r''hinovirus, and ribo''n''ucleic ''a''cid". Secondly, the name derives from ''pico''-, which designates a very small unit of measurement (equivalent to 10−12), combined with ''rna'' to describe this group of very small
RNA virus An RNA virus is a virusother than a retrovirusthat has ribonucleic acid (RNA) as its genetic material. The nucleic acid is usually single-stranded RNA ( ssRNA) but it may be double-stranded (dsRNA). Notable human diseases caused by RNA viruses ...
es.


History

The first animal virus discovered (1897) was the
foot-and-mouth disease Foot-and-mouth disease (FMD) or hoof-and-mouth disease (HMD) is an infectious and sometimes fatal viral disease that affects cloven-hoofed animals, including domestic and wild bovids. The virus causes a high fever lasting two to six days, followe ...
virus (FMDV). It is the prototypic member of the genus ''
Aphthovirus ''Aphthovirus'' (from the Greek -, vesicles in the mouth) is a viral genus of the family ''Picornaviridae''. Aphthoviruses infect split-hooved animals, and include the causative agent of foot-and-mouth disease, ''Foot-and-mouth disease virus'' ...
'' in the ''
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&nbs ...
'' family. The
plaque Plaque may refer to: Commemorations or awards * Commemorative plaque, a plate or tablet fixed to a wall to mark an event, person, etc. * Memorial Plaque (medallion), issued to next-of-kin of dead British military personnel after World War I * Pla ...
assay was developed using
poliovirus A poliovirus, the causative agent of polio (also known as poliomyelitis), is a serotype of the species ''Enterovirus C'', in the family of ''Picornaviridae''. There are three poliovirus serotypes: types 1, 2, and 3. Poliovirus is composed of an ...
; the discovery of
viral replication Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. Through the generation of abundant copies of its genome an ...
in culture was also with poliovirus in 1949. This was the first time that infectious virus had been produced in cultured cells. Polyprotein synthesis,
internal ribosome entry site An internal ribosome entry site, abbreviated IRES, is an RNA element that allows for translation initiation in a cap-independent manner, as part of the greater process of protein synthesis. In eukaryotic translation, initiation typically occurs at t ...
s, and uncapped
mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein. mRNA is ...
were all discovered by studying poliovirus infected cells, and a poliovirus clone was the first infectious DNA clone made of an
RNA virus An RNA virus is a virusother than a retrovirusthat has ribonucleic acid (RNA) as its genetic material. The nucleic acid is usually single-stranded RNA ( ssRNA) but it may be double-stranded (dsRNA). Notable human diseases caused by RNA viruses ...
in animals. Along with
rhinovirus The rhinovirus (from the grc, ῥίς, rhis "nose", , romanized: "of the nose", and the la, vīrus) is the most common viral infectious agent in humans and is the predominant cause of the common cold. Rhinovirus infection proliferates in tem ...
, poliovirus was the first animal virus to have its structure determined by
x-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
.
RNA dependent RNA polymerase RNA-dependent RNA polymerase (RdRp) or RNA replicase is an enzyme that catalyzes the replication of RNA from an RNA template. Specifically, it catalyzes synthesis of the RNA strand complementary to a given RNA template. This is in contrast to ...
was discovered in ''
Mengovirus Mengovirus, also known as Columbia SK virus, mouse Elberfield virus, and Encephalomyocarditisvirus (EMCV), belongs to the genus ''Cardiovirus'' which is a member of the ''Picornaviridae''. Its genome is a single stranded positive-sense RNA molecu ...
'', a genus of picornaviruses.


Virology


Structure

Picornaviruses are nonenveloped, with an
icosahedral In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes and . The plural can be either "icosahedra" () or "icosahedrons". There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrica ...
capsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may ...
. The capsid is an arrangement of 60
protomer In structural biology, a protomer is the structural unit of an oligomeric protein. It is the smallest unit composed of at least two different protein chains that form a larger hetero-oligomer by association of two or more copies of this unit. The ...
s in a tightly packed icosahedral structure. Each protomer consists of four polypeptides known as VP (viral protein) 1, 2, 3 and 4. VP2 and VP4 polypeptides originate from one protomer known as VP0 that is cleaved to give the different capsid components. The icosahedral is said to have a
triangulation number A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may ...
of 3, this means that in the icosahedral structure each of the 60 triangles that make up the capsid are split into three little triangles with a subunit on the corner. Many picornaviruses have a deep cleft formed by around each of the 12 vertices of icosahedrons. The outer surface of the capsid is composed of regions of VP1, VP2, and VP3. Around each of the vertices is a canyon lined with the C termini of VP1 and VP3. The interior surface of the capsid is composed of VP4 and the N termini of VP1. J. Esposito andr Freederick A. Murphy demonstrates cleft structure referred to as canyons, using X-ray crystallography and cryoelectron microscopy. Depending on the type and degree of dehydration, the viral particle is around 30–32 nm in diameter. The viral genome is around 2500 nm in length, so it is tightly packaged within the capsid along with substances such as
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
ions to balance the negative charges on the RNA caused by the
phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phospho ...
groups.


Genome

Picornaviruses are classed under Baltimore's viral classification system as group IV viruses, as they contain a single-stranded, positive-sense RNA
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
. Their genome ranges between 6.7 and 10.1 ( kilobases) in length. Like most positive-sense RNA genomes, the genetic material alone is infectious; although substantially less
virulent Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ...
than if contained within the viral particle, the RNA can have increased infectivity when transfected into cells. The genome
RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
is unusual because it has a
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
on the 5' end that is used as a
primer Primer may refer to: Arts, entertainment, and media Films * ''Primer'' (film), a 2004 feature film written and directed by Shane Carruth * ''Primer'' (video), a documentary about the funk band Living Colour Literature * Primer (textbook), a t ...
for
transcription Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including: Genetics * Transcription (biology), the copying of DNA into RNA, the fir ...
by
RNA polymerase In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that synthesizes RNA from a DNA template. Using the enzyme helicase, RNAP locally opens the ...
. This primer is called VPg genome, and it ranges between 2 and 3 kb. VPg contain tyrosine residue at the 3' end. Tyrosine as a –OH source for covalently linked to 5' end of RNA. The genome is not segmented and positive-sense (the same sense as mammalian mRNA, being read 5' to 3'). Unlike
mammalian Mammals () are a group of vertebrate animals constituting the class (biology), class Mammalia (), characterized by the presence of mammary glands which in Female#Mammalian female, females produce milk for feeding (nursing) their young, a ...
mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein. mRNA is ...
, picornaviruses do not have a 5' cap, but a virally encoded protein known as
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 Caliciviri ...
. However, like mammalian mRNA, the genome does have a
poly(A) tail Polyadenylation is the addition of a poly(A) tail to an RNA transcript, typically a messenger RNA (mRNA). The poly(A) tail consists of multiple adenosine monophosphates; in other words, it is a stretch of RNA that has only adenine bases. In euk ...
at the 3' end. An untranslated region (UTR) is found at both ends of the picornavirus genome. The 5' UTR is usually longer, being around 500–1200 nucleotides (nt) in length, compared to that of the 3' UTR, which is around 30–650 nt. The 5' UTR is thought to be important in translation, and the 3' in negative-strand synthesis; however, the 5' end may also have a role to play in virulence of the virus. The rest of the genome encodes structural proteins at the 5' end and nonstructural proteins at the 3' end in a single polyprotein. The polyprotein is organised as: L-1ABCD-2ABC-3ABCD with each letter representing a protein, but variations to this layout exist. The 1A, 1B, 1C, and 1D proteins are the capsid proteins VP4, VP2, VP3, and VP1, respectively. Virus-coded proteases perform the cleavages, some of which are intramolecular. The polyprotein is first cut to yield P1, P2, and P3. P1 becomes myristylated at the N terminus before being cleaved to VP0, VP3, and VP1, the proteins that will form procapsids; VP0 will later be cleaved to produce VP2 and VP4. Other cleavage products include 3B (VPg), 2C (an ATPase), and 3D (the RNA polymerase).


Replication


RNA elements

Genomic RNAs of picornaviruses possess multiple RNA elements, and they are required for both negative- and positive-strand RNA synthesis. The cis-acting replication element (CRE) is required for replication. The stem-loop-structure that contains the CRE is independent of position, but changes with location between virus types when it has been identified. Also, the 3' end elements of viral RNA are significant and efficient for RNA replication of picornaviruses. The 3' end of picornavirus contains poly(A) tract, which be required for infectivity. RNA synthesis, though, is hypothesized to occur in this region. The 3' end NCR of poliovirus is not necessary for negative-strand synthesis, but is important element for positive–strand synthesis. Additionally, the 5' end NCR that contains secondary structural elements is required for RNA replication and poliovirus translation initiation. Internal ribosome entry sites are RNA structures that allow cap-independent initiation of translation, and are able to initiate translation in the middle of a messenger RNA.


Lifecycle

The viral particle binds to cell surface receptors. Cell surface receptors are characterized for each serotype of picornaviruses. For example, poliovirus receptor is glycoprotein CD155, which is special receptor for human and some other primate species. For this reason, poliovirus could not be made in many laboratories until transgenic mice having a CD155 receptor on their cell surfaces were developed in the 1990s. These animals can be infected and used for studies of replication and pathogenesis. Binding causes a conformational change in the viral capsid proteins, and
myristic acid Myristic acid (IUPAC name: tetradecanoic acid) is a common saturated fatty acid with the molecular formula CH3(CH2)12COOH. Its salts and esters are commonly referred to as myristates or tetradecanoates. It is named after the binomial name for nut ...
is released. The acid forms a pore in the cell membrane through which RNA is injected. Once inside the cell, the RNA uncoats and the (+) strand RNA genome is replicated through a double-stranded RNA intermediate that is formed using viral RNA-dependent RNA polymerase. Translation by host-cell ribosomes is not initiated by a 5' G cap as usual, but rather is initiated by an internal ribosome entry site. The viral life cycle is very rapid, with the whole process of replication being completed on average within 8 hours. As little as 30 minutes after initial infection, though, cell protein synthesis declines to almost zero output – essentially the macromolecular synthesis of cell proteins is shut off. Over the next 1–2 hours, a loss of margination of
chromatin Chromatin is a complex of DNA and protein found in eukaryotic cells. The primary function is to package long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important roles in r ...
and
homogeneity Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the Uniformity (chemistry), uniformity of a Chemical substance, substance or organism. A material or image that is homogeneous is uniform in compos ...
occurs in the nucleus, before the viral proteins start to be synthesized and a vacuole appears in the cytoplasm close to the nucleus that gradually starts to spread as the time after infection reaches around 3 hours. After this time, the cell plasma membrane becomes permeable; at 4–6 hours, the virus particles assemble, and can sometimes be seen in the cytoplasm. Around 8 hours, the cell is effectively dead, and lyses to release the viral particles. Experimental data from single-step growth curve-like experiments have allowed observation of the replication of the picornaviruses in great detail. The whole of replication occurs within the host-cell cytoplasm and infection can even happen in cells that do not contain a
nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom * Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...
(enucleated) and those treated with
actinomycin D Dactinomycin, also known as actinomycin D, is a chemotherapy medication used to treat a number of types of cancer. This includes Wilms tumor, rhabdomyosarcoma, Ewing's sarcoma, trophoblastic neoplasm, testicular cancer, and certain types of ovari ...
(this antibiotic would inhibit viral replication if this occurred in the nucleus.) Translation takes place by -1 ribosomal frameshifting, viral initiation, and ribosomal skipping. The virus exits in host cell by lysis, and viroporins. Vertebrates serve as the natural hosts. Transmission routes are fecal-oral, contact, ingestion, and air-borne particles.


Viral protein (VPg)

Picornaviruses have a viral 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 Caliciviri ...
) covalently linked to 5' end of their genomes instead of 7-methylguanosine cap like cellular mRNAs. Virus RNA polymerases use VPg as primer. VPg as primer uses both positive- and negative-strand RNA synthesis. Picornavirus replication is initiated by the uridylylation of VPg. It is uridylylated at the hydroxyl group of a tyrosine residue. A VPg primer mechanism is used by the picornavirus (entero- aphtho-, and others), additional virus groups (poty-, como-, calici-, and others) and picornavirus-like (coronavirus, notavirus, etc.) supergroup of RNA viruses. The mechanism has been best studied for the enteroviruses (which include many human pathogens, such as
poliovirus A poliovirus, the causative agent of polio (also known as poliomyelitis), is a serotype of the species ''Enterovirus C'', in the family of ''Picornaviridae''. There are three poliovirus serotypes: types 1, 2, and 3. Poliovirus is composed of an ...
and coxsackie viruses), as well as for the aphthovirus, an animal pathogen causing foot-and-mouth disease. In this group, primer-dependent RNA synthesis uses a small 22– to 25-amino acid-long viral protein linked to the VPg to initiate polymerase activity, where the primer is covalently bound to the 5' end of the RNA template. The uridylylation occurs at a tyrosine residue at the third position of the VPg. A CRE, which is a RNA stem loop structure, serves as a template for the uridylylation of VPg, resulting in the synthesis of VPgpUpUOH. Mutations within the CRE-RNA structure prevent VPg uridylylation, and mutations within the VPg sequence can severely diminish RdRp catalytic activity. While the tyrosine hydroxyl of VPg can prime negative-strand RNA synthesis in a CRE- and VPgpUpUOH-independent manner, CRE-dependent VPgpUpUOH synthesis is absolutely required for positive-strand RNA synthesis. CRE-dependent VPg uridylylation lowers the K of UTP required for viral RNA replication and CRE-dependent VPgpUpUOH synthesis, and is required for efficient negative-strand RNA synthesis, especially when UTP concentrations are limiting. The VPgpUpUOH primer is transferred to the 3’ end of the RNA template for elongation, which can continue by addition of nucleotide bases by RdRp. Partial crystal structures for VPgs of foot and mouth disease virus and coxsackie virus B3 suggest that there may be two sites on the viral polymerase for the small VPgs of the picornaviruses. NMR solution structures of poliovirus VPg and VPgpU show that uridylylation stabilizes the structure of the VPg, which is otherwise quite flexible in solution. The second site may be used for uridylylation,v after which the VPgpU can initiate RNA synthesis. The VPg primers of caliciviruses, whose structures are only beginning to be revealed, are much larger than those of the picornaviruses. Mechanisms for uridylylation and priming may be quite different in all of these groups. VPg uridylylation may include the use of precursor proteins, allowing for the determination of a possible mechanism for the location of the diuridylylated, VPg-containing precursor at the 3' end of positive- or negative-strand RNA for production of full-length RNA. Determinants of VPg uridylylation efficiency suggest formation and/or collapse or release of the uridylylated product as the rate-limiting step ''in vitro ''depending upon the VPg donor employed. Precursor proteins also have an effect on VPg-CRE specificity and stability. The upper RNA stem loop, to which VPg binds, has a significant impact on both retention, and recruitment, of VPg and Pol. The stem loop of CRE will partially unwind, allowing the precursor components to bind and recruit VPg and Pol4. The CRE loop has a defined consensus sequence to which the initiation components bind, but no consensus sequence exists for the supporting stem, which suggests that only the structural stability of the CRE is important.


Assembly and organization of the picornavirus VPg ribonucleoprotein complex

# Two 3CD (VPg complex) molecules bind to CRE with the 3C domains (VPg domain) contacting the upper stem and the 3D domains (VPg domain) contacting the lower stem. # The 3C dimer opens the RNA stem by forming a more stable interaction with single strands forming the stem. # 3Dpol is recruited to and retained in this complex by a physical interaction between the back-of-the-thumb subdomain of 3Dpol and a surface of one or both 3C subdomains of 3CD. VPg may also play an important role in specific recognition of viral genome by movement proteins (MP), which are nonstructural proteins encoded by many, if not all, plant viruses to enable their movement from one infected cell to neighboring cells. MP and VPg interact to provide specificity for the transport of viral RNA from cell to cell. To fulfill energy requirements, MP also interacts with P10, which is a cellular ATPase.


Diseases

Picornaviruses cause a range of diseases. Enteroviruses of the picornavirus family infect the
enteric The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...
tract, which is reflected in their name. Rhinoviruses infect primarily the
nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passes th ...
and the
throat In vertebrate anatomy, the throat is the front part of the neck, internally positioned in front of the vertebrae. It contains the pharynx and larynx. An important section of it is the epiglottis, separating the esophagus from the trachea (windpipe ...
. Enteroviruses replicate at 37 °C, whereas
rhinovirus The rhinovirus (from the grc, ῥίς, rhis "nose", , romanized: "of the nose", and the la, vīrus) is the most common viral infectious agent in humans and is the predominant cause of the common cold. Rhinovirus infection proliferates in tem ...
es grow better at 33 °C, as this is the lower temperature of the nose. Enteroviruses are stable under acidic conditions, thus they are able to survive exposure to
gastric acid Gastric acid, gastric juice, or stomach acid is a digestive fluid formed within the stomach lining. With a pH between 1 and 3, gastric acid plays a key role in digestion of proteins by activating digestive enzymes, which together break down the ...
. In contrast, rhinoviruses are acid-labile (inactivated or destroyed by low pH conditions), so rhinovirus infections are restricted to the nose and throat.


Taxonomy

These genera are recognized: * '' Aalivirus'' * '' Ailurivirus'' * '' Ampivirus'' * '' Anativirus'' * ''
Aphthovirus ''Aphthovirus'' (from the Greek -, vesicles in the mouth) is a viral genus of the family ''Picornaviridae''. Aphthoviruses infect split-hooved animals, and include the causative agent of foot-and-mouth disease, ''Foot-and-mouth disease virus'' ...
'' * '' Aquamavirus'' * '' Avihepatovirus'' * '' Avisivirus'' * '' Boosepivirus'' * '' Bopivirus'' * '' Caecilivirus'' * ''
Cardiovirus Cardiovirus are a group of viruses within order '' Picornavirales'', family ''Picornaviridae''. Vertebrates serve as natural hosts for these viruses. Taxonomy There are currently six species in the genus: * ''Cardiovirus A'' * '' Cardiovirus B' ...
'' * '' Cosavirus'' * '' Crahelivirus'' * '' Crohivirus'' * '' Danipivirus'' * '' Dicipivirus'' * '' Diresapivirus'' * ''
Enterovirus ''Enterovirus'' is a genus of positive-sense single-stranded RNA viruses associated with several human and mammalian diseases. Enteroviruses are named by their transmission-route through the intestine ('enteric' meaning intestinal). Serologic ...
'' * ''
Erbovirus ''Erbovirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Picornaviridae''. Horses serve as natural hosts. There is only one species in this genus: ''Erbovirus A''. Diseases associated with this genus include: upper re ...
'' * '' Felipivirus'' * '' Fipivirus'' * '' Gallivirus'' * '' Gruhelivirus'' * '' Grusopivirus'' * '' Harkavirus'' * '' Hemipivirus'' * ''
Hepatovirus ''Hepatovirus'' is a genus of viruses. The genus has nine species, including ''Hepatovirus A'', which is the causative agent of hepatitis A. Taxonomy These species are recognized: * ''Hepatovirus A Hepatitis A is an infectious disease of the ...
'' * ''
Hunnivirus ''Hunnivirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Picornaviridae Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are v ...
'' * ''
Kobuvirus ''Kobuvirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Picornaviridae Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are vi ...
'' * '' Kunsagivirus'' * '' Limnipivirus'' * '' Livupivirus'' * '' Ludopivirus'' * '' Malagasivirus'' * '' Marsupivirus'' * '' Megrivirus'' * '' Mischivirus'' * ''
Mosavirus ''Mosavirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Picornaviridae Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are vi ...
'' * '' Mupivirus'' * '' Myrropivirus'' * '' Orivirus'' * ''
Oscivirus ''Oscivirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Picornaviridae Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are viru ...
'' * '' Parabovirus'' * ''
Parechovirus ''Parechovirus'' is a genus of viruses in the family ''Picornaviridae''. Humans, ferrets, and various rodents serve as natural hosts. The genus currently consists of six accepted species. Human parechoviruses may cause gastrointestinal or respira ...
'' * ''
Pasivirus ''Pasivirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Picornaviridae''. Pigs serve as natural hosts. There is only one species in this genus: ''Pasivirus A''. Structure Viruses in ''Pasivirus'' are non-enveloped, ...
'' * '' Passerivirus'' * '' Pemapivirus'' * '' Poecivirus'' * '' Potamipivirus'' * '' Pygoscepivirus'' * '' Rabovirus'' * '' Rafivirus'' * '' Rajidapivirus'' * '' Rohelivirus'' * ''
Rosavirus ''Rosavirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Picornaviridae Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are vi ...
'' * '' Sakobuvirus'' * ''
Salivirus ''Salivirus'' is a genus of viruses in the order ''Picornavirales'', in the family ''Picornaviridae''. Human and chimpanzee serve as natural hosts. There is only one species in this genus: ''Salivirus A''. Diseases associated with this genus inc ...
'' * '' Sapelovirus'' * ''
Senecavirus ''Senecavirus'' is a genus of viruses in the order '' Picornavirales'', in the family ''Picornaviridae''. Pig and maybe also cow serve as natural hosts. There is only one species in this genus: ''Senecavirus A''. ''Senecavirus'' is a replication- ...
'' * '' Shanbavirus'' * '' Sicinivirus'' * '' Symapivirus'' * '' Teschovirus'' * '' Torchivirus'' * '' Tottorivirus'' * '' Tremovirus'' * '' Tropivirus''


See also

*
Animal viruses Veterinary virology is the study of viruses in non-human animals. It is an important branch of veterinary medicine. Rhabdoviruses Rhabdoviruses are a diverse family of single stranded, negative sense RNA viruses that infect a wide range of ho ...


References


Further reading

* * *


External links

* * *
ICTV Online Report ''Picornaviridae''

ICTV International Committee on Taxonomy of Viruses Master Species Lists

ICTV International Committee on Taxonomy of Viruses (official site)


– description, replication, disease
Picornaviruses in NCBI Taxonomy browser

''Picornaviridae'' classification
by the International Committee on Taxonomy of Viruses




Virus Pathogen Database and Analysis Resource (ViPR): Picornaviridae

ICTV
{{Taxonbar, from=Q936600