Requirement for cell replication in the fixation and expression of the transformed state in mouse cells treated with 4-nitroquinoline-1-oxide.

A31-714 cells, a subclone derived from BALB/3T3, did not produce transformed foci when kept under culture conditions of density-dependent inhibition after treatment with 4NQO in either the growing or the non-growing state. The transformation frequency increased to nearly maximum level only when the cells had undergone more than four cell generations after 4NQO-treatment. Cells which were first kept in a non-growing state after 4NQO-treatment, rapidly lost the ability to exhibit transformation even when they were subsequently returned to a growing state. On the other hand, the cells which were allowed one cell replication soon after 4NQO-treatment retained their ability to produce transformed foci even after being kept in the non-growing state for as long as 6 days thereafer. These results suggest that one cell generation is required for the fixation of transformation, and more than four cell generations are required for the expression of the transformed state.