RETROVIRUSES

Description

Group of single-stranded RNA viruses that are characterized by their possessing reverse transcriptase, which transcribes the RNA genome into DNA during the replicative cycle. The transcribed viral DNA is then integrated into the host cell DNA and is replicated with it. The genomes of most retroviruses consist of a set of four genes: gag, which codes for the capsid protein of the virus; pol, which codes for the reverse transcriptase; env, which codes for a protein forming spikes on the outer envelope; onc, which is an oncogene. Many retroviruses are oncogenic, owing this property to the possession of oncogenes. Closely related sequences that are present in cellular genomes and code for normal proteins are termed proto-oncogenes. The termini of the retroviral genome consists of repeat sequences, which facilitate the integration of the retroviral DNA into the genome of the host cell. Retroviruses include Rous, Sarcoma Virus, mouse leukemia viruses such as malony leukemia virus, mouse mammary tumor viruses such as Bittner mouse milk factor virus, feline leukemia viruses, and the human HTLV viruses including the AIDS virus. Retroviruses have, in the past, been known as leucoviruses or oncornaviruses.