Picornavirus
Encyclopedia
A picornavirus is a virus
belonging to the family
Picornaviridae. Picornaviruses are non-enveloped, positive-stranded RNA viruses with an icosahedral
capsid
. The genome
RNA
is unusual because it has a protein
on the 5' end that is used as a primer
for transcription
by RNA polymerase
. The name is derived from pico, meaning small, and RNA, referring to the ribonucleic acid genome, so "picornavirus" literally means small RNA virus
.
Picornaviruses are separated into a number of genera and include many important pathogens of humans and animals. The diseases they cause are varied, ranging from acute "common-cold"-like illnesses, to poliomyelitis
, to chronic infections in livestock. Additional species not belonging to any of the recognised genera continue to be described.Lau SK, Woo PC, Lai KK, Huang Y, Yip CC, Shek CT, Lee P, Lam CS, Chan KH, Yuen KY (2011) Complete genome analysis of three novel picornaviruses from diverse bat species. J Virol.
and human pathogens, shown in the table below.
Enteroviruses infect the enteric
tract, which is reflected in their name. On the other hand, rhinovirus
es infect primarily the nose
and the throat
. Enteroviruses replicate at 37°C, whereas rhinovirus
es grow better at 33°C, as this is the lower temperature of the nose. Enteroviruses are stable under acid conditions and thus they are able to survive exposure to gastric acid
. In contrast, rhinoviruses are acid-labile (inactivated or destroyed by low pH
conditions) and that is the reason why rhinovirus infections are restricted to the nose and throat.
containing the subfamily Comovirinae (genera Comovirus, Fabavirus and Nepovirus
), and genera Sequivirus, Waikavirus, Cheravirus
, Sadwavirus
and Torradovirus (type species Tomato torrado virus)).
. Others have been placed into a new family Iflaviridae
. This family includes Infectious flacherie virus and SeIV-1 virus.
of between 7.2 and 9.0 kb (kilobases
) in length. Like most positive sense RNA genomes, the genetic material alone is infectious; although substantially less virulent than if contained within the viral particle, the RNA can have increased infectivity when transfected into cells.
is an arrangement of 60 protomers in a tightly packed Icosahedral structure. Each protometer consists of 4 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 of 3, this means that in the icosahedral structure each of the 60 triangles that make up the capsid are split into 3 little triangles with a subunit on the corner.
Depending on the type and degree of dehydration the viral particle is around 27-30 nm in diameter. The viral genome is around 2500 nm in length so we can therefore conclude that it must be tightly packaged within the capsid along with substances such as sodium
ions in order to cancel out the negative charges on the RNA caused by the phosphate
groups.
but a virally encoded protein known as VPg
. However, like mammalian mRNA, the genome does have a poly(A) tail at the 3' end. There is an un-translated region (UTR) at both ends of the picornavirus genome. The 5' UTR is longer, being around 600-1200 nucleotides (nt) in length, compared to that of the 3' UTR, which is around 50-100 nt. It is thought that the 5' UTR is 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 non-structural proteins at the 3' end in a single polyprotein.
The polyprotein is organised as follows: L-1ABCD-2ABC-3ABCD with each letter representing a protein.
The 3B protein is the VPg protein. The 3D protein is the RNA polymerase
.
are released. These acids form a pore in the cell membrane through which RNA is injectedhttp://pathmicro.med.sc.edu/virol/polio.htm. Once inside the cell, the RNA un-coats and the (+) strand RNA genome is replicated through a double-stranded RNA intermediate that is formed using viral RDRP (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 IRES (Internal Ribosome Entry Site). The viral lifecycle is very rapid with the whole process of replication being completed on average within 8 hours. However as little as 30 minutes after initial infection, cell protein synthesis declines to almost zero output – essentially the macromolecular synthesis of cell proteins is “shut off”. Over the next 1–2 hours there is a loss of margination of chromatin
and homogeneity 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. At 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 scientists to look at 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
(known as enucleated cells) and those treated with actinomycin D (this antibiotic would inhibit viral replication if this occurred in the nucleus.)
virus (FMDV), the first animal virus, was discovered. FMDV is the prototypic member of the Aphthovirus
genus in the Picornaviridae family. The plaque
assay was developed using poliovirus. Both RNA dependent RNA polymerase and polyprotein synthesis were discovered by studying poliovirus infected cells.
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
belonging to the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Picornaviridae. Picornaviruses are non-enveloped, positive-stranded RNA viruses with an icosahedral
Icosahedron
In geometry, an icosahedron is a regular polyhedron with 20 identical equilateral triangular faces, 30 edges and 12 vertices. It is one of the five Platonic solids....
capsid
Capsid
A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...
. The genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
is unusual because it has a protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
on the 5' end that is used as a primer
Primer (molecular biology)
A primer is a strand of nucleic acid that serves as a starting point for DNA synthesis. They are required for DNA replication because the enzymes that catalyze this process, DNA polymerases, can only add new nucleotides to an existing strand of DNA...
for transcription
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
by RNA polymerase
RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
. The name is derived from pico, meaning small, and RNA, referring to the ribonucleic acid genome, so "picornavirus" literally means small RNA virus
RNA virus
An RNA virus is a virus that has RNA as its genetic material. This nucleic acid is usually single-stranded RNA but may be double-stranded RNA...
.
Picornaviruses are separated into a number of genera and include many important pathogens of humans and animals. The diseases they cause are varied, ranging from acute "common-cold"-like illnesses, to poliomyelitis
Poliomyelitis
Poliomyelitis, often called polio or infantile paralysis, is an acute viral infectious disease spread from person to person, primarily via the fecal-oral route...
, to chronic infections in livestock. Additional species not belonging to any of the recognised genera continue to be described.Lau SK, Woo PC, Lai KK, Huang Y, Yip CC, Shek CT, Lee P, Lam CS, Chan KH, Yuen KY (2011) Complete genome analysis of three novel picornaviruses from diverse bat species. J Virol.
Taxonomy
Picornaviruses are separated into a number of genera. Contained within the picornavirus family are many organisms of importance as vertebrateVertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
and human pathogens, shown in the table below.
Enteroviruses infect the enteric
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
tract, which is reflected in their name. On the other hand, rhinovirus
Rhinovirus
Human rhinoviruses are the most common viral infective agents in humans and are the predominant cause of the common cold. Rhinovirus infection proliferates in temperatures between 33–35 °C , and this may be why it occurs primarily in the nose...
es infect primarily the nose
Human nose
The visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils...
and the throat
Throat
In vertebrate anatomy, the throat is the anterior part of the neck, in front of the vertebral column. It consists of the pharynx and larynx...
. Enteroviruses replicate at 37°C, whereas rhinovirus
Rhinovirus
Human rhinoviruses are the most common viral infective agents in humans and are the predominant cause of the common cold. Rhinovirus infection proliferates in temperatures between 33–35 °C , and this may be why it occurs primarily in the nose...
es grow better at 33°C, as this is the lower temperature of the nose. Enteroviruses are stable under acid conditions and thus they are able to survive exposure to gastric acid
Gastric acid
Gastric acid is a digestive fluid, formed in the stomach. It has a pH of 1 to 2 and is composed of hydrochloric acid , and large quantities of potassium chloride and sodium chloride...
. In contrast, rhinoviruses are acid-labile (inactivated or destroyed by low pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
conditions) and that is the reason why rhinovirus infections are restricted to the nose and throat.
| Genus Genus In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia... |
Species Species In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are... (* signifies type species Type species In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species... ) |
Serotypes |
|---|---|---|
| Enterovirus Enterovirus Enteroviruses are a genus of ssRNA viruses associated with several human and mammalian diseases. Serologic studies have distinguished 66 human enterovirus serotypes on the basis of antibody neutralization tests. Additional antigenic variants have been defined within several of the serotypes on the... |
Bovine enterovirus Bovine enterovirus -Introduction:Bovine enterovirus is a picornavirus of the genus enterovirus. The virus may also be referred to as enteric cytopathic bovine orphan virus . It is endemic in cattle populations and although normally fairly non-pathogenic it can cause reproductive, respiratory or enteric disease -... |
2 types: bovine enterovirus (BEV) 1-2 |
| Human enterovirus A | 21 types including some coxsackie A virus Coxsackie A virus Coxsackie A virus is a cytolytic coxsackie virus of the Picornaviridae family, an enterovirus .-Diseases:... es and enteroviruses |
|
| Human enterovirus B | 59 types including enteroviruses, coxsackie B Coxsackie B Coxsackie B is the name of a group of six serotypes of pathogenic enteroviruses that trigger illness ranging from mild gastrointestinal distress to full-fledged pericarditis and myocarditis.-Geographic distribution:... viruses, echovirus Echovirus An ECHO virus, is a type of RNA virus that belongs to the genus Enterovirus of the Picornaviridae family... es, and swine vesicular disease virus |
|
| Human enterovirus C * | 19 types including poliovirus (PV) 1-3, some coxsackie A virus Coxsackie A virus Coxsackie A virus is a cytolytic coxsackie virus of the Picornaviridae family, an enterovirus .-Diseases:... es and enteroviruses |
|
| Human enterovirus D | 3 types: EV-68, EV-70, EV-94 | |
| Porcine enterovirus B | 2 types: porcine enterovirus (PEV) 9-10 | |
| Simian enterovirus A | 1 type: simian enterovirus (SEV) A1 | |
| Human rhinovirus A * | 75 types | |
| Human rhinovirus B | 25 types | |
| Human rhinovirus C | 7+ types | |
| Cardiovirus Cardiovirus Cardiovirus is a genus within the family Picornaviridae. The genus comprises two species: Encephalomyocarditis virus and Theilovirus... |
Encephalomyocarditis virus Encephalomyocarditis virus Encephalomyocarditis virus is a member of the Picornaviridae family. Infection with the virus causes encephalomyocarditis and reproductive disease in pigs. Although a variety of mammals may host the virus, pigs are classed as the domestic host as they are most easily infected... * |
1 type: encephalomyocarditis virus (EMCV). Note: Columbia SK virus, Maus Elberfeld virus and Mengovirus Mengovirus Mengovirus, also known as Columbia SK virus, mouse Elberfield virus and Encephalomyocarditisvirus , belongs to the genus Cardiovirus which is a member of the Picornaviridae. Its genome is a single stranded positive-sense RNA molecule, making the Mengoviruses a class IV virus under the Baltimore... are strains of EMCV. |
| Theilovirus | 12 types: Theiler's murine encephalomyelitis virus Theiler's encephalomyelitis virus Theiler's Murine Encephalomyelitis Virus is a single stranded RNA murine cardiovirus from the family Picornaviridae that has been used as a mouse model for studying virally induced paralysis as well as encephalomyelitis comparable to Multiple sclerosis... (TMEV), Vilyuisk human encephalomyelitis virus (VHEV), Thera virus (TRV), Saffold virus (SAFV) 1-9 |
|
| Aphthovirus Aphthovirus Aphthovirus is a viral genus of the family Picornaviridae. Aphthoviruses infect vertebrates, and include the causative agent of foot-and-mouth disease. Foot-and-mouth disease virus is the prototypic member of the genus Aphthovirus... |
Foot-and-mouth disease Foot-and-mouth disease Foot-and-mouth disease or hoof-and-mouth disease is an infectious and sometimes fatal viral disease that affects cloven-hoofed animals, including domestic and wild bovids... virus * |
7 types: O, A, C, Southern African Territories (SAT) 1, SAT 2, SAT 3 and Asia 1 |
| Equine rhinitis A virus | 1 type: equine rhinitis A virus (ERAV) | |
| Bovine rhinitis B virus | 1 type: bovine rhinitis B virus (BRBV) | |
| Hepatovirus Hepatovirus Hepatitis is a genus of viruses belonging to the family Picornaviridae. It encompasses the Hepatitis A with one unclassified virus.-External links:*... |
Hepatitis A Hepatitis A Hepatitis A is an acute infectious disease of the liver caused by the hepatitis A virus , an RNA virus, usually spread the fecal-oral route; transmitted person-to-person by ingestion of contaminated food or water or through direct contact with an infectious person... virus * |
1 type: Hepatitis A virus (HAV) |
| Parechovirus Parechovirus Parechovirus is a viral genus in the family Picornaviridae. The genus is composed of two species: Human parechovirus and Ljungan virus.-Taxonomy:... |
Human parechovirus * | 14 types: Human parechovirus (HPeV) 1-14 |
| Ljungan virus Ljungan virus The Ljungan virus was first discovered in the mid-1990s after being isolated from a bank vole near the Ljungan river in Medelpad county, Sweden. It has since been established that the Ljungan virus, which is also found in several places in Europe and America, causes serious illness in wild as well... |
4 types: Ljungan virus (LV) 1-4 | |
| Erbovirus Erbovirus Erbovirus is a viral genus of the Picornaviridae family. Viruses belonging to the Erbovirus genus have been isolated in horses with acute upper febrile respiratory disease... |
Equine rhinitis B virus * | 3 types: equine rhinitis B virus (ERBV) 1-3 |
| Kobuvirus Kobuvirus Kobuvirus is a viral genus belonging to the family Picornaviridae. The genus is composed of three species, Aichi virus, Bovine kobuvirus and Porcine kobuvirus each possessing a single serotype... |
Aichi virus * | 1 type: Aichi virus (AiV) |
| Bovine kobuvirus | 1 type: bovine kobuvirus (BKV) | |
| Teschovirus Teschovirus The Teschovirus is a genus of the Picornaviridae family. This virus is responsible for the porcine enteroviral encephalomyelitis disease caused in pigs [1]. The Teschen disease which gave the name to the particular virus is a severe and fatal form of pig encephalomyelitis... |
Porcine teschovirus * | 11 serotypes: porcine teschovirus (PTV) 1 to 11 |
| Sapelovirus | Porcine sapelovirus * (formerly Porcine enterovirus A) | 1 type: porcine sapelovirus (PSV) (formerly PEV-8) |
| Simian sapelovirus | 3 types: simian sapleovirus (SSV) 1-3 | |
| Avian sapelovirus | 1 type: avian sapelovirus (ASV) | |
| Senecavirus | Seneca Valley virus * | 1 type: Seneca Valley virus (SVV) |
| Tremovirus | Avian encephalomyelitis virus Avian encephalomyelitis virus Avian encephalomyelitis virus, or AEV, also known epidemic tremor, is a hepatovirus belonging to the Picornavirus family.The first avian picornavirus to have its genome sequenced, it causes epidemic tremor in chickens.... |
1 type: avian encephalomyelitis virus (AEV) |
| Avihepatovirus | Duck hepatitis A virus | 3 types: duck hepatitis A virus (DHAV) 1-3 |
Plant picornaviruses
The plant picornaviruses have a number of properties that are distinct from the animal viruses. They have been classified into the family SecoviridaeSecoviridae
The Secoviridae are a family of Group IV plant-infecting viruses in the order Picornavirales.They include the following genera:*Cheravirus*Sadwavirus*Sequivirus*Torradovirus*Waikavirus...
containing the subfamily Comovirinae (genera Comovirus, Fabavirus and Nepovirus
Nepovirus
Nepoviruses or nematode transmitted polyhedral viruses, are a genus of plant viruses of the family Secoviridae and subfamily Comovirinae...
), and genera Sequivirus, Waikavirus, Cheravirus
Cheravirus
The Cheravirus refers to a genus of a plant virus in the family Secoviridae and order Picornavirales. Virus consists of a non-enveloped capsid with isometric, icosahedral symmetry...
, Sadwavirus
Sadwavirus
The Sadwavirus is a genus of a virus in the family Secoviridae in the order Picornavirales. Virion capsids are non-enveloped, round and isometric...
and Torradovirus (type species Tomato torrado virus)).
Insect picornaviruses
A number of picorna like viruses have been described infecting insects. These include Perina nuda picorna-like virus of the tussock moth, infectious flacherie virus of the silkworm and Sacbrood virus of the honeybee, Plautia stali intestine virus kelp fly virus, Ectropis obliqua picorna-like virus, deformed wing virus, acute bee paralysis virus, Drosophila C virus, Rhopalosiphum padi virus, and Himetobi P virus. Several have been placed in a separate family - the DicistroviridaeDicistroviridae
The Dicistroviridae are a family of Group IV insect-infecting viruses. Some of the insects commonly infected by dicistroviruses include aphids, leafhoppers, flies, bees, ants, silkworms.-Taxonomy:...
. Others have been placed into a new family Iflaviridae
Iflaviridae
The Iflaviridae are a family of Group IV insect-infecting viruses. Some of the insects commonly infected by dicistroviruses include aphids, leafhoppers, flies, bees, ants, silkworms, wasps....
. This family includes Infectious flacherie virus and SeIV-1 virus.
Virology
Picornaviruses are classed under Baltimore's viral classification system as group IV viruses as they contain a single stranded, positive sense RNA genomeGenome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
of between 7.2 and 9.0 kb (kilobases
Base pair
In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...
) in length. Like most positive sense RNA genomes, the genetic material alone is infectious; although substantially less virulent than if contained within the viral particle, the RNA can have increased infectivity when transfected into cells.
Structure
The capsidCapsid
A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...
is an arrangement of 60 protomers in a tightly packed Icosahedral structure. Each protometer consists of 4 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 of 3, this means that in the icosahedral structure each of the 60 triangles that make up the capsid are split into 3 little triangles with a subunit on the corner.
Depending on the type and degree of dehydration the viral particle is around 27-30 nm in diameter. The viral genome is around 2500 nm in length so we can therefore conclude that it must be tightly packaged within the capsid along with substances such as sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
ions in order to cancel out the negative charges on the RNA caused by the phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
groups.
Genome
The genome itself is the same sense as mammalian mRNA, being read 5' to 3'. Unlike mammalian mRNA picornaviruses do not have a 5' cap5' cap
The 5' cap is a specially altered nucleotide on the 5' end of precursor messenger RNA and some other primary RNA transcripts as found in eukaryotes. The process of 5' capping is vital to creating mature messenger RNA, which is then able to undergo translation...
but a virally encoded protein known as VPg
VPg
VPg is a protein attached to the 5' end of RNA during RNA synthesis in a wide variety of viruses including Picornaviridae such as Foot-and-mouth disease and poliovirus . VPg stands for "viral protein genome-linked".-Attachment during RNA synthesis:...
. However, like mammalian mRNA, the genome does have a poly(A) tail at the 3' end. There is an un-translated region (UTR) at both ends of the picornavirus genome. The 5' UTR is longer, being around 600-1200 nucleotides (nt) in length, compared to that of the 3' UTR, which is around 50-100 nt. It is thought that the 5' UTR is 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 non-structural proteins at the 3' end in a single polyprotein.
The polyprotein is organised as follows: L-1ABCD-2ABC-3ABCD with each letter representing a protein.
The 3B protein is the VPg protein. The 3D protein is the RNA polymerase
RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
.
Replication
The viral particle binds to cell surface receptors. This causes a conformational change in the viral capsid proteins, and myristic acidMyristic acid
Myristic acid, also called tetradecanoic acid, is a common saturated fatty acid with the molecular formula CH312COOH. A myristate is a salt or ester of myristic acid....
are released. These acids form a pore in the cell membrane through which RNA is injectedhttp://pathmicro.med.sc.edu/virol/polio.htm. Once inside the cell, the RNA un-coats and the (+) strand RNA genome is replicated through a double-stranded RNA intermediate that is formed using viral RDRP (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 IRES (Internal Ribosome Entry Site). The viral lifecycle is very rapid with the whole process of replication being completed on average within 8 hours. However as little as 30 minutes after initial infection, cell protein synthesis declines to almost zero output – essentially the macromolecular synthesis of cell proteins is “shut off”. Over the next 1–2 hours there is a loss of margination of chromatin
Chromatin
Chromatin is the combination of DNA and proteins that make up the contents of the nucleus of a cell. The primary functions of chromatin are; to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis and meiosis and prevent DNA damage, and to control gene...
and homogeneity 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. At 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 scientists to look at 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
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
(known as enucleated cells) and those treated with actinomycin D (this antibiotic would inhibit viral replication if this occurred in the nucleus.)
History
In 1897, foot-and-mouth diseaseFoot-and-mouth disease
Foot-and-mouth disease or hoof-and-mouth disease is an infectious and sometimes fatal viral disease that affects cloven-hoofed animals, including domestic and wild bovids...
virus (FMDV), the first animal virus, was discovered. FMDV is the prototypic member of the Aphthovirus
Aphthovirus
Aphthovirus is a viral genus of the family Picornaviridae. Aphthoviruses infect vertebrates, and include the causative agent of foot-and-mouth disease. Foot-and-mouth disease virus is the prototypic member of the genus Aphthovirus...
genus in the Picornaviridae family. The plaque
Viral plaque
A viral plaque is a visible structure formed within a cell culture, such as bacterial cultures within some nutrient medium . The bacteriophage viruses replicate and spread, thus generating regions of cell destructions known as plaques....
assay was developed using poliovirus. Both RNA dependent RNA polymerase and polyprotein synthesis were discovered by studying poliovirus infected cells.
External links
- ICTV International Committee on Taxonomy of Viruses Master Species List 2009 Version 4
- ICTV International Committee on Taxonomy of Viruses (official site)
- Picornaviruses - description, replication, disease
- Picornaviruses in NCBI Taxonomy browser
- Picornaviridae classification by the International Committee on Taxonomy of Viruses
- Animal viruses
- Viralzone: Picornaviridae
- Virus Pathogen Database and Analysis Resource (ViPR): Picornaviridae