FIG. 6.

AP-1 family members display a dynamic, temporal pattern of chromatin binding during cell cycle reentry. (A and B) chromatin-bound extracts were prepared from C10 cells at the indicated times after serum stimulation and analyzed by immunoblotting for binding of the indicated member of the AP-1 protein family. Reprobing with an antibody specific for β-actin was used to demonstrate equal loading, and a representative blot is shown. As c-Fos dissociated from chromatin and was degraded at 2 to 4 h (lanes 4 to 6), Fra-1 levels on chromatin increased and persisted until S phase (data not shown). (C) To assess the relationship between levels of nuclear c-Fos and Fra-1 and cyclin D1 expression, C10 cells were plated on glass coverslips, arrested in G₀ by serum deprivation for 72 h, and then stimulated to reenter the cell cycle by adding fresh medium with 10% FBS. Cells were fixed at the indicated times and stained for either c-Fos (green) and cyclin D1 (blue) or Fra-1 (green) and cyclin D1 (blue). Nuclei were stained with propidium iodide (red).