retrovirus

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retrovirus,

type of RNA virusvirus,
parasite with a noncellular structure composed mainly of nucleic acid within a protein coat. Most viruses are too small (100–2,000 Angstrom units) to be seen with the light microscope and thus must be studied by electron microscopes.
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 that, unlike other RNA viruses, reproduces by transcribing itself into DNA. An enzyme called reverse transcriptase allows a retrovirus's RNA to act as the template for this RNA-to-DNA transcription. The resultant DNA inserts itself into a cell's DNA and is reproduced along with the cell and its daughters. The life cycle is completed when the viral DNA in selected daughter cells makes an RNA copy of itself that covers itself in a protein coat and leaves the cell. Retroviruses sometimes destroy the cells whose DNA they alter, as with HIV, the virus that causes AIDSAIDS
or acquired immunodeficiency syndrome,
fatal disease caused by a rapidly mutating retrovirus that attacks the immune system and leaves the victim vulnerable to infections, malignancies, and neurological disorders. It was first recognized as a disease in 1981.
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, and sometimes cause them to become cancerous, as with the viruses that cause certain leukemiasleukemia
, cancerous disorder of the blood-forming tissues (bone marrow, lymphatics, liver, spleen) characterized by excessive production of immature or mature leukocytes (white blood cells; see blood) and consequently a crowding-out of red blood cells and platelets.
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. Lentiviruses are retroviruses that cause slowly progressing diseases, such as AIDS.

Retrovirus

A family of viruses distinguished by three characteristics: (1) genetic information in ribonucleic acid (RNA); (2) virions possess the enzyme reverse transcriptase; and (3) virion morphology consists of two proteinaceous structures, a dense core and an envelope that surrounds the core. Some viruses outside the retrovirus family have some of these characteristics, but none has all three. Numerous retroviruses have been described; they are found in all families of vertebrates. See Animal virus, Reverse transcriptase, Ribonucleic acid (RNA)

The genome is composed of two identical molecules of single-stranded RNA, which are similar in structure and function to cellular messenger RNA. Deoxyribonucleic acid (DNA) is not present in the virions of retroviruses. The reverse transcriptase in each virus makes a DNA copy of the RNA genome shortly after entry of the virus into the host cell. The discovery of this enzyme changed thinking in biology. Previously, the only known direction for the flow of genetic information was from DNA to RNA, yet retroviruses make DNA copies of their genome by using an RNA template. This reversal of genetic information was considered backward and hence the family name retrovirus, meaning backward virus.

Once the DNA copy of the RNA genome is made, it is inserted directly into one of the chromosomes of the host cell. This results in new genetic information being acquired by the host species. The study of reverse transcriptase has led to other discoveries of how retroviruses add a variety of new genetic information into the host. One such class of genes carried by retroviruses is oncogenes, meaning tumor genes. Retroviral oncogenes appear to be responsible for tumors in animals. See Oncogenes, Virus classification

Two distinct retroviruses have been discovered in humans. One is human T-cell lymphotropic virus type 1 (HTLV-1), a type C-like virus associated with adult T-cell leukemia. The other is the human acquired immune deficiency syndrome (AIDS) virus, a type E lentivirus. See Acquired immune deficiency syndrome (AIDS)

retrovirus

[′re·trō‚vī·rəs]
(virology)
A family of ribonucleic acid viruses distinguished by virions which possess reverse transcriptase and which have two proteinaceous structures, a dense core, and an envelope that surrounds the core.

retrovirus

A virus that is designed to avoid discovery by attacking the virus signatures or the antivirus program attempting to detect it. See virus and antivirus program.
References in periodicals archive ?
Host range and interference studies of three classes of pig endogenous retrovirus.
Extended analysis of the in vitro tropism of porcine endogenous retrovirus.
Characterization of porcine endogenous retrovirus (PERV) clones from the NIH miniature pig BAC library.
Sequence analysis of porcine endogenous retrovirus long terminal repeats and identification of transcriptional regulatory regions.
Over the past decade, an endogenous retrovirus named ERV-3 has drawn most of the attention of researchers trying to establish a role for viral proteins within the placenta.
Although ERV-3's possible placental roles continue to draw debate, another human endogenous retrovirus has popped up to steal the spotlight.
Conrad and his colleagues speculate that the production of superantigens by the activated endogenous retrovirus triggers the immune system to attack the pancreas.
Endogenous retrovirus release also has ramifications for pharmaceutical proteins made in cell substrates (e.
The companies say the study of Hormel Food and QPP pork slaughtering and processing workers will help determine whether porcine endogenous retrovirus (PERV), a virus found in all swine, is transferred to people who have a history of extensive exposure to swine tissues and fluids.
Most of those reports were suspect, she explains, because scientists could not distinguish at the time between MMTV-like viruses and human endogenous retrovirus (HER), an apparently ancient virus whose genetic code is integrated into everyone's genome.
She says her group may simply have found a novel endogenous retrovirus, though she notes that would not explain why its genetic sequences are detected only in cancer cells.