Inhibitors of this enzyme have blocked cell development in animals. Inactivating mutations of these genes leads to uncontrolled cell growth. E2F is a transcription factor that turns on genes associated with cell division. Low level of expression b. Expression restricted to certain times during the cell cycle c.
Some viruses contain v- onc that are constitutively expressed.
In the early 1900s found that retroviruses cause cancer in animals. In 1908 found erythroblastosis in chickens and 1914 found sarcoma on fowl. Viruses are extremely small microbes that pas through most filters. There are both DNA and RNA viruses, both of which lack normal cellular organization. Besides the genome, the viruses contain a few proteins that serve as structural components or to help in viral life-cycle.