Satellite (biology)

A satellite is a subviral agent composed of nucleic acid that depends on the co-infection of a host cell with a helper virus for its replication.

Satellite viruses, which are most commonly associated with plants, but are also found in mammals, arthropods, and bacteria, have the components to make their own protein shell to enclose their genetic material, but rely on a helper virus to replicate. Most viruses have the capability to use host enzymes or their own replication machinery to independently replicate their own viral RNA. Satellite viruses 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 viral genome is also dependent on the host to provide components like replicases to carry out replication. A satellite virus of mamavirus that inhibits the replication of its host has been termed a virophage. However, the usage of this term remains controversial due to the lack of fundamental differences between virophages and classical satellite viruses.

The genomes of satellite viruses range upward from 359 nucleotides in length for satellite tobacco ringspot virus RNA (STobRV).

Satellite viral particles should not be confused with satellite DNA.

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 neopvirus (TobRV) and another satellite virus. 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.

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 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. HDV is found all over the globe but is most prevalent in Africa, the Middle East and southern Italy.

Classification
Satellite viruses- satellites are classified as sub viral agents in that they require the help for co-infection; therefore, they do not have their own taxonomic classification. There is ongoing talk about proposing new genre for the taxonomic classification of satellites. 
Single-stranded RNA satellite viruses
Subgroup 1: Chronic bee paralysis virus associated satellite
Chronic bee-paralysis satellite virus
Subgroup 2: Tobacco necrosis virus satellite
Maize white line mosaic satellite virus
Panicum mosaic satellite virus
Tobacco mosaic satellite virus
Tobacco necrosis satellite virus
Double-stranded DNA satellite viruses
 Sputnik virophage
 Zamilon virophage
 Mavirus virophage
 Organic Lake virophage
Satellite nucleic acids
Single-stranded satellite DNAs
Alphasatellites
Tomato leaf curl virus satellite DNA
Betasatellites
Double-stranded satellite RNAs
Saccharomyces cerevisiae M virus satellite
Trichomonas vaginalis T1 virus satellite
Single-stranded satellite RNAs
Subgroup 1: Large satellite RNAs
Arabis mosaic virus large satellite RNA
Bamboo mosaic virus satellite RNA
Chicory yellow mottle virus large satellite RNA
Grapevine Bulgarian latent virus satellite RNA
Grapevine fanleaf virus satellite RNA
Myrobalan latent ringspot virus satellite RNA
Tomato black ring virus satellite RNA
Beet ringspot virus satellite RNA
Subgroup 2: Small linear satellite RNAs
Cucumber mosaic virus satellite RNA
Cymbidium ringspot virus satellite RNA
Pea enation mosaic virus satellite RNA
Groundnut rosette virus satellite RNA
Panicum mosaic virus small satellite RNA
Peanut stunt virus satellite RNA
Turnip crinkle virus satellite RNA
Tomato bushy stunt virus satellite RNA, B10
Tomato bushy stunt virus satellite RNA, B1
Subgroup 3: Circular satellite RNAs or "virusoids"
Arabis mosaic virus small satellite RNA
Cereal yellow dwarf virus-RPV satellite RNA
Chicory yellow mottle virus satellite RNA
Hepatitis D satellite virus RNA
Lucerne transient streak virus satellite RNA
Snake Hepatitis D virus
Solanum nodiflorum mottle virus satellite RNA
Subterranean clover mottle virus satellite RNA
Tobacco ringspot virus satellite RNA
Velvet tobacco mottle virus satellite RNA

See also

 Virus
 Virusoid
 Viroid
 Virophage
 WikiSpecies:Virus

References

External links
ICTV
Subcellular Life Forms

Category:Virology