On the proposal of a G0 phase and the restriction point

the restriction point divides the G1 phase into two parts. Cells before this point are able to leave the division cycle and enter a G0 phase; cells past this point are unaffected by a short period of low serum. Additional results of Zetterberg and Larsson—1) cy-cloheximide treatment affects cells in the same way as low serum, and 2) a delay in the second division after serum starvation in the cells not initially af-fected in their first division—indicate that their experiments are consistent with serum removal af-fecting cells in all phases of the cell cycle equally. Their experiments are consistent with the continuum model of the mammalian division cycle. There is no need to postulate a restriction point or a G0 phase to explain the serum starvation results.—Cooper, S. O