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The formation of variants with a reversion of properties of transformed cells. V. Reversion to a limited life‐span

It has been shown that hamster cells transformed after treatment with the chemical carcinogen dimethylnitrosamine (DMNA) in which the transformed state has become a hereditary cellular property, can, like cells transformed by polyoma virus, produce a high frequency of variants with a reversion of properties of transformed cells. In contrast to variants from polyoma‐transformed cells, 81–93% of the variants from DMNA‐transformed cells, and from cells transformed by benzo (a) pyrene or X‐irradiation had again, like normal cells, acquired a limited life‐span in vitro. This termination of life‐span was intracellularly determined. The escape from the limited life‐span by some of these variants was due to a re‐reversion from the reverted to the transformed state. The results suggest that the persistence of the viral genome in variants from polyoma‐transformed cells prevented their reverting to a limited life‐span.