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 ?
increased numbers of CD4 T cells specific for p24, an HIV viral capsid protein (AIDS lies Hum Retroviruses, 15:11, p.
The researchers tested blood from 418 primate handlers at 15 zoos and animal-research centers for signs of simian retroviruses.
Similarly, HIV and other retroviruses have genes made of RNA.
11th Conference on Retroviruses and Opportunistic Infections, San Francisco, February 2004 [abstract number 621].
Some retroviruses, such as the AIDS virus, HIV, enter the body from external sources.
For an overview of presentations on this subject at the Retroviruses conference, see "Pharmacogenetics Predict Abacavir (Ziagen) Hypersensitivity" by Deborah Mitchell, published March 1, 2004 on the HIV and Hepatitis site: http://www.
As the AIDS virus so tragically confirms, most retroviruses have a knack for suppressing a host's immune system.
Look for "11th Conference on Retroviruses and Opportunistic Infections," and click on one of the five major topics.
However, several small studies presented at the recent Conference on Retroviruses and Opportunistic Infections in San Francisco suggest that some people who have interrupted their therapy more than once hold down their viral concentrations, or loads, longer in later drugfree intervals.
The virus belongs to the family of retroviruses which are able to induce a persistent state in the host after acute infection.
Here are short summaries on the three experimental antiretrovirals that were most discussed at the 11th Conference on Retroviruses and Opportunistic Infections, February 8-11, 2004 in San Francisco.
Because today only HIV and a few other infectious retroviruses have a Rev protein, scientists theorized that it's a recent development in viral evolution.