Transformation by polyoma virus alters expression of a cell mutation affecting cycle traverse.

A temperature-sensitive mutant of hamster BHK 21/13 cells, tsAF8, which at 39 degrees becomes arrested in the G1 (G0) phase of the cell cycle, is phenotypically altered with respect to temperature sensitivity after transformation with polyoma virus. Polyoma transformation does not produce reversion to a non-temperature-sensitive phenotype but causes increased entry into S and increased rate of cell death at the nonpermissive temperature, compared to untransformed tsAF8 cells. The increased frequency of cells synthesizing DNA is not accompanied by an increased frequency of mitosis, since most of the polyoma-transformed tsAF8 cells that synthesize DNA at the nonpermissive temperature do not divide. At the permissive temperature, polyoma-transformed tsAF8 cells, unlike tsAF8, also lose viability when exposed to other methods of arresting cells in G1. The most likely explanation for this phenomenon is that polyoma virus transformation interferes with the cellular response to this mutation as well as to other conditions that cause cell cycle arrest in G1.