Positive-strand RNA virus

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Positive-strand RNA virus
HCV EM picture 2.png
Hepatitis C virus
Virus classification
Group:
Group IV ((+)ssRNA)
Kingdom: Phylum: Class
Synonyms
  • Positive-sense RNA virus

Positive-strand RNA viruses (+ssRNA viruses) are a group of related viruses that have positive-sense, single-stranded genomes made of ribonucleic acid. The positive-sense genome can act as messenger RNA (mRNA) and can be directly translated into viral proteins by the host cell's ribosomes. Positive-strand RNA viruses encode an RNA-dependent RNA polymerase (RdRp) which is used during replication of the genome to synthesize a negative-sense antigenome that is then used as a template to create a new positive-sense viral genome.

Contents

Positive-strand RNA viruses are divided between the phyla Kitrinoviricota , Lenarviricota , and Pisuviricota (specifically classes Pisoniviricetes and Stelpavirictes ) all of which are in the kingdom Orthornavirae and realm Riboviria . [1] They are monophyletic and descended from a common RNA virus ancestor. In the Baltimore classification system, +ssRNA viruses belong to Group IV. [2]

Positive-sense RNA viruses include pathogens such as the Hepatitis C virus, West Nile virus, dengue virus, and the MERS, SARS, and SARS-CoV-2 coronaviruses, [3] as well as less clinically serious pathogens such as the coronaviruses and rhinoviruses that cause the common cold. [4] [5] [6]

Genome

Positive-strand RNA virus genomes usually contain relatively few genes, usually between three and ten, including an RNA-dependent RNA polymerase. [4] Coronaviruses have the largest known RNA genomes, between 27 and 32 kilobases in length, and likely possess replication proofreading mechanisms in the form of an exoribonuclease within nonstructural protein nsp14. [7]

Replication

Life cycle of Japanese encephalitis virus a +ssRNA virus: attachment, endocytosis, membrane fusion, uncoating, translation, RNA replication, assembly, maturation, and release. Pathogens-07-00068-g002.webp
Life cycle of Japanese encephalitis virus a +ssRNA virus: attachment, endocytosis, membrane fusion, uncoating, translation, RNA replication, assembly, maturation, and release.

Positive-strand RNA viruses have genetic material that can function both as a genome and as messenger RNA; it can be directly translated into protein in the host cell by host ribosomes. [8] The first proteins to be expressed after infection serve genome replication functions; they recruit the positive-strand viral genome to viral replication complexes formed in association with intracellular membranes. These complexes contain proteins of both viral and host cell origin, and may be associated with the membranes of a variety of organelles—often the rough endoplasmic reticulum, [9] but also including membranes derived from mitochondria, vacuoles, the Golgi apparatus, chloroplasts, peroxisomes, plasma membranes, autophagosomal membranes, and novel cytoplasmic compartments. [4]

The replication of the positive-sense RNA genome proceeds through double-stranded RNA intermediates, and the purpose of replication in these membranous invaginations may be the avoidance of cellular response to the presence of dsRNA. In many cases subgenomic RNAs are also created during replication. [8] After infection, the entirety of the host cell's translation machinery may be diverted to the production of viral proteins as a result of the very high affinity for ribosomes by the viral genome's internal ribosome entry site (IRES) elements; in some viruses, such as poliovirus and rhinoviruses, normal protein synthesis is further disrupted by viral proteases degrading components required to initiate translation of cellular mRNA. [6]

All positive-strand RNA virus genomes encode RNA-dependent RNA polymerase, a viral protein that synthesizes RNA from an RNA template. Host cell proteins recruited by +ssRNA viruses during replication include RNA-binding proteins, chaperone proteins, and membrane remodeling and lipid synthesis proteins, which collectively participate in exploiting the cell's secretory pathway for viral replication. [4]

Recombination

Mechanisms of replicative and nonreplicative RNA recombination. Viruses-11-00859-g004.png
Mechanisms of replicative and nonreplicative RNA recombination.

Numerous positive-strand RNA viruses can undergo genetic recombination when at least two viral genomes are present in the same host cell. [10] The capability for recombination among +ssRNA virus pathogens of humans is common. RNA recombination appears to be a major driving force in determining genome architecture and the course of viral evolution among Picornaviridae (e.g. poliovirus). [11] In the Retroviridae (e.g. HIV), genome damage appears to be avoided during reverse transcription by strand switching, a form of recombination. [12] [13] [14] Recombination occurs in the Coronaviridae (e.g. SARS). [15] Recombination in RNA viruses appears to be an adaptation for coping with genome damage. [10] Recombination can also occur infrequently between +ssRNA viruses of the same species but of divergent lineages. The resulting recombinant viruses may sometimes cause an outbreak of infection in humans, as in the case of SARS and MERS. [15]

Positive-strand RNA viruses are common in plants. In tombusviruses and carmoviruses, RNA recombination occurs frequently during replication. [16] The ability of the RNA-dependent RNA polymerase of these viruses to switch RNA templates suggests a copy choice model of RNA recombination that may be an adaptive mechanism for coping with damage in the viral genome. [16] Other +ssRNA viruses of plants have also been reported to be capable of recombination, such as Brom mosaic bromovirus [17] and Sindbis virus. [18]

Classification

Phylogenetic tree with phylum branches highlighted. Negarnaviricota (brown), Duplornaviricota (green), Kitrinoviricota (pink), Pisuviricota (blue), and Lenarviricota (yellow). MBio.02329-18.F1.large.jpg
Phylogenetic tree with phylum branches highlighted. Negarnaviricota (brown), Duplornaviricota (green), Kitrinoviricota (pink), Pisuviricota (blue), and Lenarviricota (yellow).

Positive-strand RNA viruses are found in three phyla: Kitrinoviricota, Lenarviricota, and Pisuviricota, each of which are assigned to the kingdom Orthornavirae in the realm Riboviria . In the Baltimore classification system, which groups viruses together based on their manner of mRNA synthesis, +ssRNA viruses are group IV.[ citation needed ]

Kitrinoviricota

The first +ssRNA phylum is Kitrinoviricota . The phylum contains what have been referred to as the "alphavirus supergroup" and "flavivirus supergroup" along with various other short-genome viruses. Four classes in the phylum are recognized: Alsuviricetes , the alphavirus supergroup, which contains a large number of plant viruses and arthropod viruses; Flasuviricetes, which contains flaviviruses, Magsaviricetes , which contains nodaviruses and sinhaliviruses; and Tolucaviricetes , which primarily contains plant viruses. [19] [20]

Lenarviricota

Lenarviricota is the second +ssRNA phylum. It contains the class Leviviricetes , which infect prokaryotes, and the apparent descendants of leviviruses, which infect eukaryotes. The phylum is divided into four classes: Leviviricetes, which contains leviviruses and their relatives, Amabiliviricetes, which contains narnaviruses and their relatives, Howeltoviricetes, which contains mitoviruses and their relatives, and Miaviricetes, which contains botourmiaviruses and their relatives. Based on phylogenetic analysis of RdRp, all other RNA viruses are considered to comprise a sister clade in relation to Lenarviricota. [19] [20]

Pisuviricota

False-color Transmission electron micrograph of a SARS-CoV-2 virion. Coronaviruses like SARS-CoV-2 fall in the phylum Pisuviricota. Novel Coronavirus SARS-CoV-2 (50960620707) (cropped).jpg
False-color Transmission electron micrograph of a SARS-CoV-2 virion. Coronaviruses like SARS-CoV-2 fall in the phylum Pisuviricota .

The third phylum that contains +ssRNA viruses is Pisuviricota , which has been informally called the "picornavirus supergroup". The phylum contains a large assemblage of eukaryotic viruses known to infect animals, plants, fungi, and protists. The phylum contains three classes, two of which contain only +ssRNA viruses: Pisoniviricetes , which contains nidoviruses, picornaviruses, and sobeliviruses, and Stelpaviricetes , which contains potyviruses and astroviruses. The third class is Duplopiviricetes , whose members are double-stranded RNA viruses that are descended from +ssRNA viruses. [19] [20]

See also

Related Research Articles

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<span class="mw-page-title-main">RNA virus</span> Subclass of viruses

An RNA virus is a virus characterized by a ribonucleic acid (RNA) based genome. The genome can be single-stranded RNA (ssRNA) or double-stranded (dsRNA). Notable human diseases caused by RNA viruses include influenza, SARS, MERS, COVID-19, Dengue virus, hepatitis C, hepatitis E, West Nile fever, Ebola virus disease, rabies, polio, mumps, and measles.

Virus classification is the process of naming viruses and placing them into a taxonomic system similar to the classification systems used for cellular organisms.

<i>Parvoviridae</i> Family of viruses

Parvoviruses are a family of animal viruses that constitute the family Parvoviridae. They have linear, single-stranded DNA (ssDNA) genomes that typically contain two genes encoding for a replication initiator protein, called NS1, and the protein the viral capsid is made of. The coding portion of the genome is flanked by telomeres at each end that form into hairpin loops that are important during replication. Parvovirus virions are small compared to most viruses, at 23–28 nanometers in diameter, and contain the genome enclosed in an icosahedral capsid that has a rugged surface.

<span class="mw-page-title-main">SARS-related coronavirus</span> Species of coronavirus causing SARS and COVID-19

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<span class="mw-page-title-main">Picornavirus</span> Family of viruses

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 icosahedral capsid. The viruses in this family can cause a range of diseases including the common cold, poliomyelitis, meningitis, hepatitis, and paralysis.

<i>Bunyavirales</i> Order of RNA viruses

Bunyavirales is an order of segmented negative-strand RNA viruses with mainly tripartite genomes. Member viruses infect arthropods, plants, protozoans, and vertebrates. It is the only order in the class Ellioviricetes. The name Bunyavirales derives from Bunyamwera, where the original type species Bunyamwera orthobunyavirus was first discovered. Ellioviricetes is named in honor of late virologist Richard M. Elliott for his early work on bunyaviruses.

<i>Geminiviridae</i> Family of viruses

Geminiviridae is a family of plant viruses that encode their genetic information on a circular genome of single-stranded (ss) DNA. There are 520 species in this family, assigned to 14 genera. Diseases associated with this family include: bright yellow mosaic, yellow mosaic, yellow mottle, leaf curling, stunting, streaks, reduced yields. They have single-stranded circular DNA genomes encoding genes that diverge in both directions from a virion strand origin of replication. According to the Baltimore classification they are considered class II viruses. It is the largest known family of single stranded DNA viruses.

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<i>Nidovirales</i> Order of positive-sense, single-stranded RNA viruses

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Baltimore classification is a system used to classify viruses based on their manner of messenger RNA (mRNA) synthesis. By organizing viruses based on their manner of mRNA production, it is possible to study viruses that behave similarly as a distinct group. Seven Baltimore groups are described that take into consideration whether the viral genome is made of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), whether the genome is single- or double-stranded, and whether the sense of a single-stranded RNA genome is positive or negative.

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<span class="mw-page-title-main">RNA-dependent RNA polymerase</span> Enzyme that synthesizes RNA from an RNA template

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 typical DNA-dependent RNA polymerases, which all organisms use to catalyze the transcription of RNA from a DNA template.

<i>Cowpea chlorotic mottle virus</i> Species of virus

Cowpea chlorotic mottle virus, known by the abbreviation CCMV, is a virus that specifically infects the cowpea plant, or black-eyed pea. The leaves of infected plants develop yellow spots, hence the name "chlorotic". Similar to its "brother" virus, Cowpea mosaic virus (CPMV), CCMV is produced in high yield in plants. In the natural host, viral particles can be produced at 1–2 mg per gram of infected leaf tissue. Belonging to the bromovirus genus, cowpea chlorotic mottle virus (CCMV) is a small spherical plant virus. Other members of this genus include the brome mosaic virus (BMV) and the broad bean mottle virus (BBMV).

<span class="mw-page-title-main">Double-stranded RNA viruses</span> Type of virus according to Baltimore classification

Double-stranded RNA viruses are a polyphyletic group of viruses that have double-stranded genomes made of ribonucleic acid. The double-stranded genome is used as a template by the viral RNA-dependent RNA polymerase (RdRp) to transcribe a positive-strand RNA functioning as messenger RNA (mRNA) for the host cell's ribosomes, which translate it into viral proteins. The positive-strand RNA can also be replicated by the RdRp to create a new double-stranded viral genome.

<span class="mw-page-title-main">Negative-strand RNA virus</span> Phylum of viruses

Negative-strand RNA viruses are a group of related viruses that have negative-sense, single-stranded genomes made of ribonucleic acid (RNA). They have genomes that act as complementary strands from which messenger RNA (mRNA) is synthesized by the viral enzyme RNA-dependent RNA polymerase (RdRp). During replication of the viral genome, RdRp synthesizes a positive-sense antigenome that it uses as a template to create genomic negative-sense RNA. Negative-strand RNA viruses also share a number of other characteristics: most contain a viral envelope that surrounds the capsid, which encases the viral genome, −ssRNA virus genomes are usually linear, and it is common for their genome to be segmented.

<i>Riboviria</i> Realm of viruses

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In virology, realm is the highest taxonomic rank established for viruses by the International Committee on Taxonomy of Viruses (ICTV), which oversees virus taxonomy. Six virus realms are recognized and united by specific highly conserved traits:

<i>Monodnaviria</i> Realm of viruses

Monodnaviria is a realm of viruses that includes all single-stranded DNA viruses that encode an endonuclease of the HUH superfamily that initiates rolling circle replication of the circular viral genome. Viruses descended from such viruses are also included in the realm, including certain linear single-stranded DNA (ssDNA) viruses and circular double-stranded DNA (dsDNA) viruses. These atypical members typically replicate through means other than rolling circle replication.

<i>Orthornavirae</i> Kingdom of viruses

Orthornavirae is a kingdom of viruses that have genomes made of ribonucleic acid (RNA), including genes which encode an RNA-dependent RNA polymerase (RdRp). The RdRp is used to transcribe the viral RNA genome into messenger RNA (mRNA) and to replicate the genome. Viruses in this kingdom share a number of characteristics which promote rapid evolution, including high rates of genetic mutation, recombination, and reassortment.

References

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