TAILIEUCHUNG - Chapter 181. The Human Retrovirusesviruses, which make up a large family

The retroviruses, which make up a large family (Retroviridae), infect mainly vertebrates. These viruses have a unique replication cycle whereby their genetic information is encoded by RNA rather than DNA. Retroviruses contain an RNA-dependent DNA polymerase (a reverse transcriptase) that directs the synthesis of a DNA form of the viral genome after infection of a host cell. The designation retrovirus denotes that information in the form of RNA is transcribed into DNA in the host cell—a sequence that overturned a central dogma of molecular biology: that information passes unidirectionally from DNA to RNA to protein. . | Chapter 181. The Human Retroviruses Introduction The retroviruses which make up a large family Retroviridae infect mainly vertebrates. These viruses have a unique replication cycle whereby their genetic information is encoded by RNA rather than DNA. Retroviruses contain an RNA-dependent DNA polymerase a reverse transcriptase that directs the synthesis of a DNA form of the viral genome after infection of a host cell. The designation retrovirus denotes that information in the form of RNA is transcribed into DNA in the host cell a sequence that overturned a central dogma of molecular biology that information passes unidirectionally from DNA to RNA to protein. The observation that RNA was the source of genetic information in the causative agents of certain animal tumors led to a number of paradigmshifting biologic insights regarding not only the direction of genetic information passage but also the viral etiology of certain cancers and the concept of oncogenes as normal host genes scavenged and altered by a viral vector. The family Retroviridae includes three subfamilies Table 181-1 Oncovirinae of which human T cell lymphotropic virus HTLV type I is the most important in humans Lentivirinae of which HIV is the most important in humans and Spumavirinae the quot foamy quot viruses named for the pathologic appearance of infected cells. A number of spumaviruses have been isolated from humans however they are not associated with any known disease and therefore are not discussed further in this chapter. Table 181-1 Classification of Retroviruses The Family Retroviridae Subfamily Group Example s Feature Oncovirinae oncogenic viruses Avian leukosis Rous sarcoma virus Contains src oncogene Mammalian C-type Abelson leukemia virus Contains abl oncogene B-type Murine mammary tumor virus Can be endogenous or exogenous D-type Mason-Pfizer monkey virus HTLV-BLV HTLV-I Lentivirinae slow HIV-1 HIV-2 viruses Visna virus Causes T-cell lymphoma and neurologic disease Cause AIDS Causes .

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