Final answer:
Proto-oncogenes can be converted to oncogenes by viruses through three main mechanisms: viral genome insertion near proto-oncogenes, viral-oncogene expression, and interference with gene expression.
Step-by-step explanation:
Proto-oncogenes can be converted to oncogenes by viruses through three main mechanisms:
- Viral genome insertion near proto-oncogenes: In slowly-transforming viruses, the virus genome is inserted near a proto-oncogene in the host genome. The viral promoter or other transcription regulation elements cause overexpression of the proto-oncogene, leading to uncontrolled cellular proliferation.
- Viral-oncogene (v-onc) expression: Acutely transforming viruses carry a gene that encodes for an overactive oncogene called viral-oncogene (v-onc). When the virus infects a cell, v-onc is expressed and immediately transforms the cell.
- Interference with gene expression: Some oncogenic viruses interfere with the normal regulation of the host cell cycle. They introduce genes that stimulate unregulated cell growth (oncogenes) or interfere with the expression of genes that inhibit cell growth.