Virology

RETROVIRIDAE FAMILY

Written by MicroDok

Retroviridae family is a unique family of viruses that contain reverse transcriptase (RT) which allows all viruses in this family to carryout reverse transcription of their genome. Viruses in this family are usually referred to as retroviruses because of their possession of RT. Retroviruses are distributed worldwide. Reverse transcription is the genetic process of copying the genetic information found in the RNA genome of an organism into DNA. Viruses in this family cause various types of tumours, lymphomas or sarcomas in animals. And this implies that some retroviruses are oncogenic or cancer-causing in nature. Retroviruses also infect invertebrates as well as vertebrates. Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) which causes AIDS and simian AIDS in humans and monkeys respectively are the most important viruses in the Retroviridae family.

Viruses in the Retroviridae family have an icosahedral shape; and they measure between 80-110 nm in diameter. They possess a ss(+)RNA, and they replicate in the nucleus of their host cell. Retroviruses are enveloped viruses, and their envelope is rich in lipids and proteins. Retroviruses are released via the process of budding from the cytoplasmic membrane of their host cell. There are seven (7) genera of viruses in the Retroviridae family. These viral genera are Lentivirus, Spumavirus, Epsilonretrovirus, Betaretrovirus, Alpharetrovirus, Deltaretrovirus and Gammaretrovirus. HIV and SIV, which are one of the most significant viruses in this family, are found in the genus Lentivirus. The human T-cell leukemia virus-1 (HTLV-1), a Deltaretrovirus is another important member of the Retroviridae family which causes lymphoma in humans. With the help of reverse transcriptase, the ssRNA genome of retroviruses is transcribed by RT into a dsDNA molecule otherwise known as provirus or viral DNA.

The provirus is finally integrated into the chromosomal DNA of the host cell; and the viral DNA surmounts or takes over the cellular machinery of their host cell to produce viral RNAs and protein molecules required for the formation of new virions. It is noteworthy that the provirus generally serves as the template for the biosynthesis of viral RNA and protein molecules that are required for the assembling of new viral progenies (i.e. new retroviruses). Infections or diseases caused by retroviruses especially AIDS still have no permanent cure but the disease can be clinically managed or treated using some antiviral drugs such as zidovudine or azidothymidine (AZT) which are nucleoside analogs that inhibit the activities of RT during the replication of retroviruses.               

SELECTED REFERENCES

Acheson N.H (2011). Fundamentals of Molecular Virology. Second edition. John Wiley and Sons Limited, West Sussex, United Kingdom.

Ahmad K (2002). Norwalk-like virus attacks troops in Afghanistan. Lancet Infect Dis, 2:391.

Alan J. Cann (2005). Principles of Molecular Virology. 4th edition. Elsevier Academic Press,   Burlington, MA, USA.

Alba R, Bosch A and Chillon M (2005). Gutless adenovirus: last-generation adenovirus for gene therapy. Gene Ther, Suppl 12:S18-S27.

Alberts B, Bray D, Johnson A, Lewis J, Raff M, Roberts K and Walter P (1998). Essential Cell Biology: An Introduction to the Molecular Biology of the Cell. Third edition. Garland Publishing Inc., New York.

Balows A, Hausler W, Herrmann K.L, Isenberg H.D and Shadomy H.J (1991). Manual of clinical microbiology. 5th ed. American Society of Microbiology Press, USA.

Barrett   J.T (1998).  Microbiology and Immunology Concepts.  Philadelphia,   PA: Lippincott-Raven Publishers. USA.

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MicroDok

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