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Information about Retro Virus

Retroviruses
Virus classification
Group:Group VI (ssRNA-RT)
Family:Retroviridae
Genera
Alpharetrovirus
Betaretrovirus
Gammaretrovirus
Deltaretrovirus
Epsilonretrovirus
Lentivirus
Spumavirus
A retrovirus is any virus belonging to the viral family Retroviridae. They are enveloped viruses possessing a RNA genome, and replicate via a DNA intermediate. Retroviruses rely on the enzyme reverse transcriptase to perform the reverse transcription of its genome from RNA into DNA, which can then be integrated into the host's genome with an integrase enzyme. The virus then replicates as part of the cell's DNA.

Description of virus

The virus itself stores its nucleic acid, in the form of a +mRNA (including the 5'cap and 3'PolyA inside the virion) genome and serves as a means of delivery of that genome into cells it targets as an obligate parasite, and constitutes the infection. Once in the host's cell, the RNA strands undergo reverse transcription in the cytosol and are integrated into the host's genome, at which point the retroviral DNA is referred to as a provirus.

Reproduction

When retroviruses have integrated their genome into the germ line, their genome is passed on to a following generation. These endogenous retroviruses, contrasted with exogenous ones, now make up 0.03% of the human genome[1]. Most insertions have no known function and are often referred to as "junk DNA". However, many endogenous retroviruses play important roles in host biology, such as control of gene transcription, cell fusion during placental development in the course of the germination of an embryo, and resistance to exogenous retroviral infection. Endogenous retroviruses have also received special attention in the research of immunology-related pathologies, such as autoimmune diseases like multiple sclerosis, although endogenous retroviruses have not yet been proven to play any causal role in this class of disease. The role of endogenous retroviruses in human gene evolution is explored in a 2005 peer-reviewed article.[2]

While transcription was classically thought to only occur from DNA to RNA, reverse transcriptase transcribes RNA into DNA. The term "retro" in retrovirus refers to this reversal (making DNA from RNA) of the central dogma of molecular biology. Reverse transcriptase activity outside of retroviruses has been found in almost all eukaryotes, enabling the generation and insertion of new copies of retrotransposons into the host genome. It is important to note that a retrovirus must "bring" its own reverse transcriptase in its capsid, otherwise it is unable to utilize the infected cell's enzymes to carry out the task, due to the unusual nature of producing DNA from RNA.

Because reverse transcription lacks the usual proofreading of DNA replication, this kind of virus mutates very often. This enables the virus to grow resistant to antiviral pharmaceuticals quickly, and impedes, for example, the development of an effective vaccine against the retrovirus HIV.

Genes

Retrovirus genomes commonly contain these three open reading frames that encode for proteins that can be found in the mature virus:

Clinical significance

Thus far, four human retroviruses — HTLV 1 and 2, in conjunction with HIV 1 and 2 have been found to attack Helper T cells.

Development of retroviruses

Studies of retroviruses led to the first demonstrated synthesis of DNA from RNA templates, a fundamental mode for transferring genetic material that occurs in both eukaryotes and prokaryotes.

It has been speculated that the RNA to DNA transcription processes used by retroviruses may have first caused DNA to be used as genetic material.

In this model, the RNA world hypothesis, cellular organisms adopted the more chemically stable DNA when retroviruses evolved to create DNA from the RNA templates.

Classification

Exogenous

The following genera are included here: These were previously divided into three subfamilies (Oncovirinae, Lentivirinae, and Spumavirinae), but with current knowledge of retroviruses, this is no longer appropriate. (The term oncovirus is still commonly used, though.)

Endogenous

Main article: endogenous retrovirus
Endogenous retroviruses are not formally included in this classification system, and are broadly classified into three classes, on the basis of relatedness to exogenous genera:
  • Class I are most similar to the gammaretroviruses
  • Class II are most similar to the betaretroviruses and alpharetroviruses
  • Class III are most similar to the spumaviruses

See also

References

1. ^ Robert Belshaw; Pereira V; Katzourakis A; Talbot G; Paces J; Burt A; Tristem M. (April 2004). "Long-term reinfection of the human genome by endogenous retroviruses". Proc Natl Acad Sci U S A 101 (14): 4894–99. PMID 15044706. 
2. ^ Medstrand P, van de Lagemaat L, Dunn C, Landry J, Svenback D, Mager D (2005). "Impact of transposable elements on the evolution of mammalian gene regulation". Cytogenet Genome Res 110 (1-4): 342-52. PMID 16093686. 

External links

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RNA viruses: retroviruses
Virus classification involves naming and placing viruses into a taxonomic system. Like the relatively consistent classification systems seen for cellular organisms, virus classification is the subject of ongoing debate and proposals.
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A reverse transcribing virus is any virus which replicates using reverse transcription, the formation of DNA from an RNA template. Both Group VI and Group VII viruses fall into this category.
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An alpharetrovirus is a genus of the retroviridae family. It has type C morphology. Members can cause sarcomas, other tumors, and anaemia of wild and domestic birds and also affect rats.
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A betaretrovirus is a genus of the retroviridae family. It has type B or type C morphology. The type B is common for a few exogenous, vertically transmitted and endogenous viruses of mice, some primate and sheep viruses are the type D.
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A gammaretrovirus is a genus of the retroviridae family. Many species contain oncogenes and cause sarcomas and leukemias.

Examples are the murine leukemia virus, the feline leukemia virus, the feline sarcoma virus, and the avian reticuloendotheliosis viruses.
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A deltaretrovirus is a genus of the retroviridae family. It consists of exogenous horizontally-transmitted viruses found in several groups of mammals.

Examples are the bovine leukaemia virus and the Human T-lymphotropic virus.
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An epsilonretrovirus is a genus of the retroviridae family. It infects fish. The species include the Walleye dermal sarcoma virus, and Walleye epidermal hyperplasia virus 1 and 2.
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Lentivirus (lenti-, Latin for "slow") is a genus of slow viruses of the Retroviridae family, characterized by a long incubation period. Lentiviruses can deliver a significant amount of genetic information into the DNA of the host cell, so they are
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spumavirus or foamyvirus is a genus of the retroviridae family. Spumaviruses are exogenous viruses that have specific morphology with prominent surface spikes. The virions contain significant amounts of double-stranded full-length DNA, and assembly is rather unusual in these
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Left: An RNA strand, with its nitrogenous bases. Right: Double-stranded DNA.]] Ribonucleic acid or RNA is a nucleic acid polymer consisting of nucleotide monomers, which plays several important roles in the processes of translating genetic information from
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In biology the genome of an organism is its whole hereditary information and is encoded in the DNA (or, for some viruses, RNA). This includes both the genes and the non-coding sequences of the DNA.
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In biochemistry, a reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase enzyme that transcribes single-stranded RNA into single-stranded DNA.
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Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. So to say, it is the transfer of genetic information from DNA into RNA.
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Integrase is an enzyme produced by a retrovirus (including HIV) that enables its genetic material to be integrated into the DNA of the infected cell. It is also produced by viruses containing double stranded DNAs for the same purpose.
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An obligate parasite is an organism that cannot live independently of its host. For example, a virus is an obligate parasite because it cannot reproduce outside a host cell.

References

  • Serge, Morand. et al. (1996).

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An infection is the detrimental colonization of a host organism by a foreign species. In an infection, the infecting organism seeks to utilize the host's resources to multiply (usually at the expense of the host).
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Reverse transcription is the process of making a double stranded DNA (deoxyribonucleic acid) molecule from a single stranded RNA (ribonucleic acid) template. It is called reverse transcription as it acts in the opposite or reverse direction to transcription.
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The cytosol (cf. cytoplasm, which also includes the organelles) is the internal fluid of the cell, and a portion of cell metabolism occurs here. Proteins within the cytosol play an important role in signal transduction pathways and glycolysis.
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A provirus is a virus genome that has integrated itself into the DNA of a host cell. One kind of virus that can become a provirus is a retrovirus. When a retrovirus invades a cell, the RNA of the retrovirus is transcribed into DNA by reverse transcriptase, then inserted into the
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In biology and genetics, the germline of a mature or developing individual is the line (sequence) of germ cells that have genetic material that may be passed to a child.

For example, sex cells, such as the sperm or the egg, are part of the germline.
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Inheritance is the practice of passing on property, titles, debts, and obligations upon the death of an individual. It has long played an extremely important role in human societies.

Both anthropology and sociology have made detailed studies in this area.
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Endogenous retroviruses are retroviruses derived from ancient infections of germ cells in humans, mammals and other vertebrates; as such their proviruses are passed on to the next generation and now remain in the genome.
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Exogenous DNA refers to any deoxyribonucleic acid, which originates outside of the organism of concern or study.

The introduction of exogenous DNA into a cell is called transfection. This can take place naturally, as occurs when a virus infects cells, or artificially.
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In molecular biology, "junk" DNA is a collective label for the portions of the DNA sequence of a chromosome or a genome for which no function has yet been identified. About 80-90% of the human genome has been designated as "junk", including most sequences within introns and most
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The placenta is an ephemeral (temporary) organ present in placental vertebrates, such as some mammals and sharks during gestation (pregnancy).

The placenta develops from the same sperm and egg cells that form the fetus, and functions as a fetomaternal organ with two
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Germination is the process where growth emerges from a period of dormancy. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm.
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