Origin of Retroviruses
It is common to speak of viruses as autonomous genetic elements, dependent on cell machinery for replication, at least in part, but consisting of an RNA or DNA genome unrelated in nucleotide sequence to genes of its host. It does not necessarily follow that virus genomes which are unrelated to cell genes did not originate from them. If the genome of a given virus evolved independently of the cellular genes the degree of virus-cell homology would depend on the rate of virus-cell divergenee since the origination event and the elapsed time. RNA tumor viruses offer a unique model for studying the origination of viruses from cell genes, for it appears that many existing RNA tumor viruses originated recently from cellular genes. Indeed, retroviruses can in many instances be derived from uninfected cells in the laboratory.
KeywordsLeukemia Virus Bovine Leukemia Virus Mouse Mammary Tumor Virus Rous Sarcoma Virus Papio Cynocephalus
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