Growth state of the cell early after infection with simian virus 40 determines whether the maintenance of transformation will be A-gene dependent or independent.

The existence of both temperature-sensitive (N) and temperature-insensitive (A) rat transformants, isolated after infection with simian virus 40 tsA mutant, is reported. Both types can be isolated as dense foci. Foci appearing after infection of rapidly growing cells were temperature sensitive. Infection of cells arrested at confluence gave rise to foci that were temperature insensitive. Transformants isolated by the agar assay (conditions under which normal cells are unable to grow) were also temperature-insensitive. N-transformants remained temperature sensitive upon entering the resting state at the restrictive temperature and upon re-entering the growth cycle at the permissive temperature. They also remained temperature sensitive under a variety of conditions restrictive for nontransformed cells. Thus, the state of the cell in the first few days after infection fixes the cells. Thus, the state of the cell in the first few days after infection fixes the cell as an N- or A-transformant. Various models for transformation are discussed, including one proposing that the virus interacts in two ways with a central cell mechanism controlling growth. The maintenance of the transformed phenotype would be dependent on T-antigen in N-transformants but independent of T-antigen in A-transformants.