Induction of C-Type Particles in Mammalian Cancer Cells
Temin postulated (1,2) that the viral DNA synthesized by the oncorna virion-associated reverse transcriptase (3,4) integrates into the host cell DNA as an essential step in the cellular transformation process. The studies of Hill and Hillova, who demonstrated that permissive cells were transformed by purified DNA molecules from transformed cells (5), confirmed Temin’s hypothesis. Thus, the oncorna virus-transformed cell contains viral DNA sequences in the cellular genome. The mechanism which leads to the integration of the viral DNA molecules into the cellular DNA is not yet known. Also, the cellular mechanisms which control the expression of the viral DNA are not yet understood. In permissive cells, transformation is accompanied by virus production, while in nonpermissive cells transformation occurs but without virus production. These findings suggest that in nonpermissive cells, the transcription of the viral DNA is controlled by the host cell process. Although the viral DNA is repressed in the nonpermissive cells, it was demonstrated (6) that virus synthesis could be induced by fusion of transformed cells with permissive cells. Treatment with 5-bromodeoxyuridine (BUdR) also induced virus replication (7), similar to the effect of arginine deprivation on nonpermissive cells (8). Although the mechanism of virus induction is not understood, the induction of virus replication was used to study the presence of oncorna viruses in cancer cells.
KeywordsSucrose Gradient Cytosine Arabinoside Rous Sarcoma Virus Virus Release Permissive Cell
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