Question

1. How do viral oncogenes occur?

2. How do viral oncogenes cause cancer (what is the general mechanism)?

Please do not copy and paste an incorrect answer. Thumbs down for such atrocity.

Answer 1

1, Viral oncogenes are those genes present in the viral genetic material which has the ability to cause cancer. they can convert the normal healthy cell into oncogenic cells. There are DNA containing oncoviruses such as hepatitis-B virus and RNA containing oncovruses such as Simian Virus 40.

Herald Varmous and Michael Bishop in 1976 made a remarkable contribution about the origin of oncogenes in oncovirus from their studies in which they compared the genes in normal chicken cells and oncogenes of Rous Sarcoma virus and demonstrated the similarity between them. They concluded that the retroviruses get the oncogenes from cellular normal genes during replication.

This exactly means that the virus through replication and budding from the host cells acquires some normal host cellular gene (ex- Src genes). These normal genes found in the cell of host are now called as proto-oncogenes.They are responsible for normal functions such as synthesising growth factors, signals, etc required for development of normal cells. The change in the proto-oncogenes by means of mutation (gain of function mutation)  or genetic re-arrangement in oncoviruses causes the formation of oncogenes ( mostly retrovirus). Oncogenes are termed as v-oncogene and proto-oncogenes are termed as c-oncogene (c for cellular).

So the viral oncogenes origin from mutation in normal cellular proto-oncogenes. This particular viral oncogene has no function to play for viral survival such as replication. they are mostly retroviruses.

there are other viruses whch has oncogenes as their integral part of the genome required for replication. They are mostly DNA viruses.