EXPERIMENTAL FIGURE 24-22 Addition of serum to quiescent 3T3 cells yields a marked increase in the activity of two proto-oncogene products, FOS and MYC. Serum contains factors such as platelet-derived growth factor (PDGF) that stimulate the growth of quiescent cells. One of the earliest effects of growth factors is to induce expression of FOS and MYC, whose encoded proteins are transcription factors.

[Data from M. E. Greenberg and E. B. Ziff, 1984, Nature 311:433.]