A family of RNA viruses 80–100 nm in diameter, enveloped, and containing two identical molecules of positive sense, single-stranded RNA, molecular weight 3–6 × 106; genomic RNA serves as a template for the synthesis of a complementary DNA, which may be integrated into the host DNA. There are currently 7 genera : Mammalian type B retroviruses, Mammalian type C retroviruses, Avian type C retroviruses, Type D retroviruses, BLV-HTLV retroviruses, Lentivirus, and Spumovirus.
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Ret·ro·vi·ri·dae .re-trō-'vir-ə-.dē n pl a family of single-stranded RNA viruses that produce reverse transcriptase by means of which DNA is synthesized using their RNA as a template and incorporated into the genome of infected cells, that are often tumorigenic, and that include the foamy viruses, HIV, HTLV-I, Rous sarcoma virus, SIV, and the causative agents of avian leukosis, equine infectious anemia, ovine progressive pneumonia, and jaagsiekte see lentivirus
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Ret·ro·vi·ri·dae (ret″ro-virґĭ-de) the retroviruses: a family of RNA viruses having a virion 80–100 nm in diameter consisting of a lipid-containing envelope with peplomers, surrounding an icosahedral capsid. The genome consists of two identical molecules of polyadenylated positive-sense single-stranded RNA; the monomers are connected at the 5′ end by hydrogen bonds and each has a molecular weight of approximately 3 Ч 106 and a size of 3.5–9 kb, depending on the genus. Viruses contain seven major polypeptides, including a reverse transcriptase, and are resistant to ultraviolet light but sensitive to lipid solvents and detergents. Replication is unique: genomic RNA serves as a template for DNA synthesis via reverse transcriptase; complementary DNA is synthesized from viral DNA and integrated into the host cell DNA, where it is used for transcription. Assembly occurs by budding through the plasma membrane. Most retroviruses are oncogenic. Genera of medical or veterinary importance are Alpharetrovirus, Betaretrovirus, Gammaretrovirus, Deltaretrovirus, Lentivirus, and Spumavirus.Medical dictionary. 2011.