Induction of the nuclear protein cyclin in serum-stimulated quiescent 3T3 cells is independent of DNA synthesis.

Inhibition of DNA synthesis and cell proliferation of mouse 3T3 cells by aphidicolin did not affect the expression of cyclin, a nuclear protein whose synthesis correlates with cell proliferation, as determined by quantitative two-dimensional gel electrophoresis analysis. Serum stimulation of quiescent 3T3 cells revealed that cyclin synthesis increases shortly before DNA synthesis. Inhibition of DNA synthesis by aphidicolin in serum-stimulated quiescent cells did not affect the increase of cyclin following stimulation. These results demonstrate that cyclin synthesis is not coupled to DNA synthesis and that it is one of the latest events before DNA replication.