Chickens could get cancer from a filterable extract of tumors. Translated to make reverse transcriptase. DNA copy made, with duplication of ends to make LTR at each end. Circular form goes to nucleus and integrates at random location. Stays there forever.
Transcription makes new copies.
35o but not 41o. Temp sensitive mutants due to mutant protein that is unstable at high temps. A certain amount of mutation at this point would give a v-onc surrounded by LTRs. Other scenarios possible. Showed that oncogenes in human tumors are the same as oncogenes idnetified from retroviruses.