How were oncogenes first discovered?
Oncogenes were first discovered in retroviruses that cause cancer (also called RNA tumor viruses). The genome of a retrovirus is an RNA molecule. When a retrovirus infects a cell, it makes a DNA copy of its RNA, which is then integrated into the genome of the cell. The integrated piece of DNA then produces proteins required for the production of more viruses. Certain kinds of cancer in chickens were found to be caused by an infectious agent. This infectious agent turned out to be a retrovirus, which was given the name Rous sarcoma virus. The Rous sarcoma virus can also infect and transform tissue culture cells, which made it possible to carry out extensive experiments to determine how the virus causes transformation. Initial experiments established that the Rous sarcoma virus carries a gene that causes cancer. This gene was given the name src. Later experiments demonstrated that the src gene is an altered version of a gene normally found within cells. These experiments led to the cruci
