[DNA form of the genome of oncornaviruses]

The oncornaviruses share several biological, biochemical, and structural properties that distinguish them from other RNA viruses. Rous sarcoma virus, a representative of avian oncornaviruses, manifests two major functions: cell transformation and virus replication. Both functions are independent, and are expressed separately in defective viruses. The virus has a 60-70S RNA, composed of 35 S subunits. It appears that each subunit of viral RNA carries the same genetic information and, furthermore, that 10% of this information is coding for cell transformation. Without this 10% the virus can still replicate. The RNA genome is expressed when the virus penetrates a sensitive cell, provided the virus carries an active reverse transcriptase. Virus-transformed cells possess a DNA form of the viral genome. The viral DNA is infectious, and can lead, upon transfection of permissive cells, to the production of a new viral progeny. We have established that the minimum molecular weight of the viral DNA is 6 X 10(6) daltons, and that this DNA is covalently bound to the chromosomal DNA. Also by examining the frequency of transfection events in the DNA-treated cells we suggest that transfection is a single-hit phenomenon. It follows that viral DNA of 6 X 10(6) daltons carries all the genetic information to code for the virus production. It seems likely that the transfection mechanism giving rise to transforming viruses is different from that producing nontransforming segments. In general terms, the experimental data indicate that certain RNAs and DNAs could accomplish malignant transformation if they are able to penetrate into the cell and give rise to the DNA forms which could be integrated into the cellular genome.