Transformation by a temperature sensitive mutant of Rous sarcoma virus in the absence of serum

Cultures of chicken embryo fibroblasts infected with the temperature-sensitive transformation mutant of Rous sarcoma virus, tsLA24PR-A, were arrested between mitosis and S phase by exposure to serum-free medium at the non-permissive temperature (41degree C) for 2 days. On shifting to the permissive temperature (35degree C) the cells assumed a transformed morphology and increased uptake of [2minus 3H]-Deoxy-glucose. There was a concomitant increase in acid insoluble [3H]-thymidine. This suggests that the virus transforming function can cause stationary cells to enter their growth cycle. The level of release of infectious virus was shown to decrease on cell cycle arrest in serum-free medium and not to recover on a shift to 35 degrees, when cellular DNA synthesis and transformation was induced. Cultures rendered stationary in medium containing serum depleted of multiplication stimulating factor did not show this reduction in virus production.