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What was the Rous sarcoma virus, and why was it important to cancer research?

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Diagram illustrating the process of retrovirus infection and reverse transcription, showing a retrovirus entering a host cell, releasing viral RNA, reverse transcriptase converting RNA to DNA, integration into the host genome, transcription of new viral RNA, assembly of new virions, and budding from the cell. — Reverse transcriptase After a retrovirus infects a cell, an enzyme known as reverse transcriptase converts viral RNA into proviral DNA in the cytoplasm. Proviral DNA then enters the nucleus, where it is incorporated into the host cell's DNA.

The Rous sarcoma virus (RSV) is a retrovirus that causes sarcomas—malignant tumors of connective tissue—in chickens. First described by American pathologist Peyton Rous in 1911, it was the first virus identified as a cause of cancer in animals.123

RSV is of fundamental importance to cancer research for several reasons:

Discovery of Oncogenes: Researchers identified that RSV carries a specific gene, src, which is responsible for transforming normal cells into cancerous ones. This was the first identified oncogene. Scientists later discovered that src was not originally a viral gene but a host cellular gene (proto-oncogene) that the virus had accidentally acquired. This breakthrough revealed that cancer can arise from the mutation or dysregulation of normal genes involved in cell growth.43
Discovery of Reverse Transcriptase: The study of RSV led to the 1970 discovery of reverse transcriptase, an enzyme that transcribes viral RNA into DNA. This discovery challenged the "central dogma" of molecular biology and provided the basis for understanding how retroviruses integrate their genetic material into host cells.42
Laboratory Tool: RSV has served as a vital model for studying the molecular genetics of cancer, helping scientists understand how viral infection and genetic integration lead to malignant transformation.34