Satellite (biology)

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Satellite
Satellite tobacco mosaic virus crystal.jpg
In (a) is an orthorhombic crystal of satellite tobacco mosaic virus (STMV) that is more than 1.5 mm in length and was about 30 times the volume of any STMV crystal ever grown on Earth. It was grown in the Cryostat instrument on International Microgravity Laboratory-1. In (b) is an equivalent sized cubic crystal of the same virus, again, far exceeding in dimensions any grown in an Earth laboratory.
Scientific classification
(unranked):
Subviral agents
(unranked):
Satellite
Groups
  • Satellite viruses
  • Satellite nucleic acids

A satellite is a subviral agent that depends on the coinfection of a host cell with a helper virus for its replication. Satellites can be divided into two major classes: satellite viruses and satellite nucleic acids. [1] Satellite viruses, which are most commonly associated with plants, are also found in mammals, arthropods, and bacteria. They encode structural proteins to enclose their genetic material, which are therefore distinct from the structural proteins of their helper viruses. [1] Satellite nucleic acids, in contrast, do not encode their own structural proteins, but instead are encapsulated by proteins encoded by their helper viruses. [1] [2] The genomes of satellites range upward from 359 nucleotides in length for satellite tobacco ringspot virus RNA (STobRV). [3]

Contents

Most viruses have the capability to use host enzymes or their own replication machinery to independently replicate their own viral RNA. Satellites, in contrast, are completely dependent on a helper virus for replication. The symbiotic relationship between a satellite and a helper virus to catalyze the replication of a satellite genome is also dependent on the host to provide components like replicases [4] to carry out replication. [5]

A satellite virus of mamavirus that inhibits the replication of its host has been termed a virophage. [6] However, the usage of this term remains controversial due to the lack of fundamental differences between virophages and classical satellite viruses. [7]

History and discovery

The tobacco necrosis virus was the virus that led to the discovery of the first satellite virus in 1962. Scientists discovered that the first satellite had the components to make its own protein shell. A few years later in 1969, scientists discovered another symbiotic relationship with the tobacco ringspot nepovirus (TobRV) and another satellite virus. [8] The emergence of satellite RNA is said to have come from either the genome of the host or its co-infecting agents, and any vectors leading to transmission. [9]

A satellite virus important to human health that demonstrates the need for co-infection to replicate and infect within a host is the virus that causes hepatitis D. Hepatitis D or delta virus (HDV) was discovered in 1977 by Mario Rizzetto [10] and is differentiated from hepatitis A, B, and C because it requires viral particles from hepatitis B virus (HBV) to replicate and infect liver cells. HBV provides a surface antigen, HBsAg, which is utilized by HDV to create a super-infection resulting in liver failure. [11] HDV is found all over the globe but is most prevalent in Africa, the Middle East and southern Italy. [11]

Satellite compared to a virus

Satellite compared to a virus
SatelliteVirus
ReplicationDepend on the presence of host cells and helper viruses to replicate their genomesDepend on the presence of host cells to replicate their genomes
Nucleic acidContain DNA or RNAContain DNA or RNA, or both at different points in life cycle
Genome size0.22 to 1.5 kb10 kb to 1.5 Mb
StructureSatellite viruses encode their own protein capsids with the aid of helper viruses

Satellite nucleic acids do not have capsids, but rely on helper viruses to enclose their genomes

Package their genome within a capsid (protein shell)

Have an envelope (not all viruses)

Host rangePlants (most common), mammals, arthropods, bacteriaCan infect all types of organism; animals, plants, fungi, bacteria, archaea

Classification

The classification of subviral agents is ongoing. The following uses an outline for subviral agents in a 2011 ICTV report. [1] A lot of the taxa have since been assigned more formal names in 2019, so these are included when possible.

Satellite viruses

Some satellite viruses have been assigned a taxon. The following reflects the results of a 2015 proposal that has since been accepted (Taxoprop 2015.009a). [12]

Satellite nucleic acids

The following may not be comprehensive in its ICTV coverage. The nomenclature for satellite RNAs is to prefix the host virus name with "sat".

Satellite-like nucleic acids resemble satellite nucleic acids, in that they replicate with the aid of helper viruses. However they differ in that they can encode functions that can contribute to the success of their helper viruses; while they are sometimes considered to be genomic elements of their helper viruses, they are not always found within their helper viruses.

See also

Related Research Articles

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

An RNA virus is a virus—other than a retrovirus—that 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 include the common cold, influenza, SARS, MERS, COVID-19, Dengue virus, hepatitis C, hepatitis E, West Nile fever, Ebola virus disease, rabies, polio, mumps, and measles.

Viroids are small single-stranded, circular RNAs that are infectious pathogens. Unlike viruses, they have no protein coating. All known viroids are inhabitants of angiosperms, and most cause diseases, whose respective economic importance to humans varies widely. A recent metatranscriptomics study suggests that the host diversity of viroids and other viroid-like elements is broader than previously thought and that it would not be limited to plants, encompassing even the prokaryotes.

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

Hepatitis D is a type of viral hepatitis caused by the hepatitis delta virus (HDV). HDV is one of five known hepatitis viruses: A, B, C, D, and E. HDV is considered to be a satellite because it can propagate only in the presence of the hepatitis B virus (HBV). Transmission of HDV can occur either via simultaneous infection with HBV (coinfection) or superimposed on chronic hepatitis B or hepatitis B carrier state (superinfection).

Virusoids are circular single-stranded RNA(s) dependent on viruses for replication and encapsidation. The genome of virusoids consists of several hundred (200–400) nucleotides and does not code for any proteins.

<i>Tombusviridae</i> Family of viruses

Tombusviridae is a family of single-stranded positive sense RNA plant viruses. There are three subfamilies, 17 genera, and 95 species in this family. The name is derived from Tomato bushy stunt virus (TBSV).

<i>Tobamovirus</i> Genus of viruses

Tobamovirus is a genus of positive-strand RNA viruses in the family Virgaviridae. Many plants, including tobacco, potato, tomato, and squash, serve as natural hosts. Diseases associated with this genus include: necrotic lesions on leaves. The name Tobamovirus comes from the host and symptoms of the first virus discovered.

<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).

<i>Totivirus</i> Genus of viruses

Totivirus is a genus of double-stranded RNA viruses in the family Totiviridae. Fungi serve as natural hosts. The name of the group derives from Latin toti which means undivided or whole. There are seven species in this genus.

<i>Nepovirus</i> Genus of viruses

Nepovirus is a genus of viruses in the order Picornavirales, in the family Secoviridae, in the subfamily Comovirinae. Plants serve as natural hosts. There are 40 species in this genus. Nepoviruses, unlike the other two genera in the subfamily Comovirinae, are transmitted by nematodes.

<span class="mw-page-title-main">Hairpin ribozyme</span> Enzymatic section of RNA

The hairpin ribozyme is a small section of RNA that can act as a ribozyme. Like the hammerhead ribozyme it is found in RNA satellites of plant viruses. It was first identified in the minus strand of the tobacco ringspot virus (TRSV) satellite RNA where it catalyzes self-cleavage and joining (ligation) reactions to process the products of rolling circle virus replication into linear and circular satellite RNA molecules. The hairpin ribozyme is similar to the hammerhead ribozyme in that it does not require a metal ion for the reaction.

<i>Sobemovirus</i> Genus of viruses

Sobemovirus is a genus of non-enveloped, positive-strand RNA viruses which infect plants. Plants serve as natural hosts. There are 21 species in this genus. Diseases associated with this genus include: mosaics and mottles.

<i>Potexvirus</i> Genus of viruses

Potexvirus is a genus of pathogenic viruses in the order Tymovirales, in the family Alphaflexiviridae. Plants serve as natural hosts. There are 48 species in this genus, three of which are assigned to a subgenus. Diseases associated with this genus include: mosaic and ringspot symptoms. The genus name comes from POTato virus X).

<i>Carlavirus</i> Genus of viruses

Carlavirus, formerly known as the "Carnation latent virus group", is a genus of viruses in the order Tymovirales, in the family Betaflexiviridae. Plants serve as natural hosts. There are 53 species in this genus. Diseases associated with this genus include: mosaic and ringspot symptoms.

<span class="mw-page-title-main">Positive-strand RNA virus</span> Class of viruses in the Baltimore classification

Positive-strand RNA 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.

<i>Riboviria</i> Realm of viruses

Riboviria is a realm of viruses that includes all viruses that use a homologous RNA-dependent polymerase for replication. It includes RNA viruses that encode an RNA-dependent RNA polymerase, as well as reverse-transcribing viruses that encode an RNA-dependent DNA polymerase. RNA-dependent RNA polymerase (RdRp), also called RNA replicase, produces RNA from RNA. RNA-dependent DNA polymerase (RdDp), also called reverse transcriptase (RT), produces DNA from RNA. These enzymes are essential for replicating the viral genome and transcribing viral genes into messenger RNA (mRNA) for translation of viral proteins.

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>Varidnaviria</i> Realm of viruses

Varidnaviria is a realm of viruses that includes all DNA viruses that encode major capsid proteins that contain a vertical jelly roll fold. The major capsid proteins (MCP) form into pseudohexameric subunits of the viral capsid, which stores the viral deoxyribonucleic acid (DNA), and are perpendicular, or vertical, to the surface of the capsid. Apart from this, viruses in the realm also share many other characteristics, such as minor capsid proteins (mCP) with the vertical jelly roll fold, an ATPase that packages viral DNA into the capsid, and a DNA polymerase that replicates the viral genome.

<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.

<span class="mw-page-title-main">Ribozyviria</span> Realm of viruses

Ribozyviria is a realm of satellite nucleic acids — infectious agents that resemble viruses, but cannot replicate without a helper virus. Established in ICTV TaxoProp 2020.012D, the realm is named after the presence of genomic and antigenomic ribozymes of the Deltavirus type. The agents in Ribozyviria are satellite nucleic acids, which are distinct from satellite viruses in that they do not encode all of their own structural proteins but require proteins from their helper viruses in order to assemble. Additional common features include a rod-like structure, an RNA-binding "delta antigen" encoded in the genome, and animal hosts. Furthermore, the size range of the genomes of these viruses is between around 1547–1735nt, they encode a hammerhead ribozyme or a hepatitis delta virus ribozyme, and their coding capacity only involves one conserved protein. Most lineages of this realm are poorly understood, the notable exception being the genus Deltavirus, comprising the causal agents of hepatitis D in humans.

References

  1. 1 2 3 4 "3 – Satellites and Other Virus-dependent Nucleic Acids – Subviral Agents – Subviral Agents (2011)". International Committee on Taxonomy of Viruses (ICTV). (newer version; does not mention satellites [ dead link ])
  2. ↑ Baez, John. "Subcellular Life Forms". University of California, Riverside. Retrieved 4 June 2020.
  3. ↑ Wayne L. Gerlach; Jamal M. Buzayan; Irving R. Schneider; George Bruening (1986). "Satellite Tobacco Ringspot Virus RNA: Biological Activity of DNA Clones and Their in Vitro Transcripts". Virology. 151 (2): 172–185. doi:10.1016/0042-6822(86)90040-1. PMID   18640636.
  4. ↑ Hu, Chung-Chi; Hsu, Yau-Heiu; Lin, Na-Sheng (18 December 2009). "Satellite RNAs and Satellite Viruses of Plants". Viruses. 1 (3): 1325–1350. doi: 10.3390/v1031325 . PMC   3185516 . PMID   21994595.
  5. ↑ Krupovic, Mart; Kuhn, Jens H.; Fischer, Matthias G. (1 January 2016). "A classification system for virophages and satellite viruses". Archives of Virology. 161 (1): 233–247. doi: 10.1007/s00705-015-2622-9 . hdl: 11858/00-001M-0000-0028-DC34-F . ISSN   0304-8608. PMID   26446887.
  6. ↑ Bernard La Scola; Christelle Desnues; Isabelle Pagnier; Catherine Robert; Lina Barrassi; Ghislain Fournous; Michèle Merchat; Marie Suzan-Monti; Patrick Forterre; Eugene Koonin & Didier Raoult (2008). "The virophage as a unique parasite of the giant mimivirus". Nature. 455 (7205): 100–4. Bibcode:2008Natur.455..100L. doi:10.1038/nature07218. PMID   18690211. S2CID   4422249.
  7. ↑ Krupovic M; Cvirkaite-Krupovic V (2011). "Virophages or satellite viruses?". Nat Rev Microbiol. 9 (11): 762–763. doi:10.1038/nrmicro2676. PMID   22016897. S2CID   41271832.
  8. ↑ Roossinck, M. J.; Sleat, D.; Palukaitis, P. (June 1992). "Satellite RNAs of plant viruses: structures and biological effects". Microbiological Reviews. 56 (2): 265–279. doi:10.1128/MMBR.56.2.265-279.1992. ISSN   0146-0749. PMC   372867 . PMID   1620065.
  9. ↑ Hu, Chung-Chi; Hsu, Yau-Heiu; Lin, Na-Sheng (2009). "Satellite RNAs and Satellite Viruses of Plants". Viruses. 1 (3): 1325–1350. doi: 10.3390/v1031325 . PMC   3185516 . PMID   21994595.
  10. ↑ "Hepatitis D Virus". web.stanford.edu. Retrieved 1 December 2017.
  11. 1 2 "Hepatitis D: Background, Etiology, Epidemiology". Medscape. Retrieved 1 December 2017.
  12. ↑ Krupovic, Mart; Kuhn, Jens H.; Fischer, Matthias G. (7 October 2015). "A classification system for virophages and satellite viruses". Archives of Virology. 161 (1): 233–247. doi: 10.1007/s00705-015-2622-9 . hdl: 11858/00-001M-0000-0028-DC34-F . PMID   26446887.
  13. ↑ Taxoprop 2017.004P
  14. ↑ Taxoprop 2016.021a-kP
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