Messenger RNAs coding for enzymes of polyamine biosynthesis are induced during the G0-G1 transition but not during traverse of the normal G1 phase.

The events occurring during emergence of cells from quiescence ("G0") are not necessarily identical to those in the G1 phase of continuously dividing cells. Cellular levels of the mRNAs coding for ornithine decarboxylase (ODC) and S-adenosyl-methionine decarboxylase (SDC), key enzymes in polyamine synthesis, increased maximally within 5 h after addition of serum to resting 3T3 cells, following a kinetic course similar to that of c-myc mRNA. In a pure early G1 population of cells, prepared by centrifugal elutriation of growing fibroblasts, the levels of ODC and SDC mRNAs were not significantly lower than in other phases of the cell cycle and approximated serum-induced levels rather than the reduced values found in serum-starved cells. Thus, we conclude that the mRNAs coding for the polyamine biosynthetic enzymes, like c-myc, are growth controlled, but not regulated during traverse of a normal cell cycle.