Resting state in normal and simian virus 40 transformed Chinese hamster lung cells

Normal cell deprived of amino acids or serum factors enter a resting state, whereas cells transformed by wild-type simian virus 40 do not. The ability to enter a resting state is temperature-sensitive (ts) in cells transformed by a tsA mutant of simian virus 40. We shown further: (i) that when complete medium is added to resting cells, the length of time until the onset of DNA synthesis often exceeds the length of G1 in growing cells; (ii) that the length of this interval depends upon the conditions used to arrest cell growth; but (iii) that transferring cultures from medium depleted for one factor to medium depleted in a second factor never leads to a round of DNA synthesis; and (iv) that DNA synthesis does not resume rapidly when a resting culture of cells transformed by the tsA mutant is transferred to the permissive temperature in suboptimal medium. A model proposing that in suboptimal conditions cells leave the cell cycle and traverse a branch pathway to enter the resting state is consistent with these findings.