FIG. 4.

Synchronization of NIH 3T3 cells by serum starvation and stimulation. Cells were serum starved (0.5% BCS) for 48 to 60 h and then stimulated to reenter the cell cycle by the addition of 10% serum. At 0, 8, 12, and 16 h after serum stimulation, cells were trypsinized, ethanol fixed, and stained with propidium iodide. The DNA content of each population of cells was measured by flow cytometry analysis. As a reference, analysis of a population of asynchronous cells which were not starved and stimulated (log) is also included. IP, immunoprecipitation.