The list of proto-oncogenes identified to date is too lengthy to include here, therefore, only those genes that have been highly characterized are described. Recessive and the genes variously termed tumor suppressors, growth suppressors, recessive oncogenes or anti-oncogenes. This suspicion has proven true with the identification of numerous genes, whose products function in cellular signaling, that are involved in some way in the genesis of the tumorigenic state. Tumor viruses are of two distinct types. RNA tumor viruses are common in chickens, mice and cats but rare in humans.
Retroviruses can induce the transformed state within the cells they infect by two mechanisms.
Both of these mechanisms are related to the life cycle of these viruses. The DNA then integrates into the genome of the host cell where it can remain being copied as the host genome is duplicated during the process of cellular division. The LTRs promote the transcription of the viral DNA leading to the production of new virus particles. At some frequency the integration process leads to rearrangement of the viral genome and the consequent incorporation of a portion of the host genome into the viral genome. This process is termed transduction.