- Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.
- Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.
- 9. Transducing retroviruses form due to random integration of proviral DNA.
- a. If proviral insertion causes a genetic rearrangement that connects viral transcription signals to nearby cellular sequences:
- i. All viral progeny will carry and express the cellular sequence.
- ii. If the acquired sequence is an oncogene, the virus will be oncogenic.
- iii. If the acquired sequence is a proto-oncogene that shows increased expression when in the viral genome, the virus will also be oncogenic.
- iv. Viral sequences are often deleted in the process.
- b. An example of how a transducing virus may form (Figure 18.11):
- i. A retrovirus integrates near a cellular proto-oncogene.
- ii. A deletion fuses retrovirus sequences with proto-oncogene sequences.
- iii. TranscriptIon (and splicing if necessary) produces a fusion mRNA.
- iv. Normal retrovirus genome and the fusion mRNA are copackaged, providing reverse transcriptase that can switch templates and make a defective transducing virus.
- c. Evidence that viral oncogenes derive from transduced cellular proto-oncogenes:
- i. Cellular proto-oncogenes are in conserved positions on the chromosome, but viral oncogenes are in variable positions.
- ii. Cellular homologs of v-onc genes are conserved between species, but v-onc genes are not conserved between viral strains.
- iii. Transduction can be accomplished experimentally in tissue culture and in animals.
Fig. 18.11 Model for the formation of a transducing retrovirus - Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.
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