Retroviruses containing inserts

Cellular oncogenes (VI) can be activated by amplification, by single point mutations, or by transposition. Slowly transforming retroviruses do not contain viral oncogenes but stimulate expression of cellular oncogenes by insertional mutagenicity. Radiation and chemical carcinogens also activate cellular onco-... 

After a retrovirus Infects a cell, reverse transcription of Its RNA genome by the retrovirus-encoded reverse transcriptase yields a double-stranded DNA containing complete LTRs (Figure 10-13). Integrase, another enzyme encoded by retroviruses that Is closely related to the trans-posase of some DNA transposons, uses a similar mechanism to Insert the double-stranded retroviral DNA Into the hostcell genome. In this process, short direct repeats of the target-site sequence are generated at either end of the Inserted viral DNA sequence. 

Part or all of the viral genome becomes linearly inserted into chromosomes of transformed cells. For RNA viruses like Rous sarcoma virus, the viral genome must be converted to double-strand DNA before this insertion can occur. The viral enzyme that synthesizes DNA from a single-strand RNA template is called reverse transcriptase, and viruses containing reverse transcriptase are called retroviruses (see here). 

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