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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.
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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)

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


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.
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References in periodicals archive ?
Moore, "No evidence for infection of human cells with porcine endogenous retrovirus (PERV) after exposure to porcine fetal neuronal cells," Transplantation, vol.
Staege, "Expression and regulation of the endogenous retrovirus 3 in Hodgkin's lymphoma cells," Frontiers in Oncology, vol.
The endogenous retrovirus mysTR was originally identified in the white-footed mouse Peromyscus leucopus [35].
EBV may also alter the immune response in bystander cells through induced expression of a HERV (human endogenous retrovirus) superantigen by the viral LMP2A protein also expressed during viral latency (left).
Absence of replication of porcine endogenous retrovirus and porcine lymphotropic herpesvirus type 1 with prolonged pig cell microchimerism after pig-to-baboon xenotransplantation.
Pig endogenous retrovirus (PERV) is one of many known and unknown infectious agents that may be transferred via animal-to-human transplants.
In vito studies are needed to determine which porcine cells produce porcine endogenous retrovirus (PERV) and which human cells are sensitive to PERV.
L-PCR further substantiated primer specificity (Figure 4; Table 1) by demonstrating no cross-reactivity (amplicon generation) by using template DNA from cell lines harboring representatives of all mammalian and avian oncogenic retroviral subfamilies and human lentiviruses; viruses previously reported in human breast tissues (Epstein-Barr virus, human papillomavirus, mouse mammary tumor virus-like sequences) (17); and human endogenous retrovirus HERV-K (Table 1).
CpG methylation of the LTRs of human endogenous retrovirus (HERV-K) (Lavie et al., 2005) and proviral HIV have been shown to suppress transcription (Bednarik et al., 1987).
Porcine endogenous retrovirus, or PERV, is perhaps the most worrisome of these viruses.
The most serious concern is that of cross-species retroviral infection--that porcine endogenous retrovirus (PERV) will possibly combine with human endogenous retrovirus and result in a new recombinant virus that is capable of causing disease and being transmitted among humans.
I realize that such articles aren't comprehensive reviews of the literature, but I must point out that we have recently published in VIRUS GENES direct experimental evidence that supports the involvement of endogenous retrovirus in embryo implantation.