UV exposure-dependent increase of the hRad9 association to the p53-binding site in the P21 promoter. (A) Schematic representation of the P21 promoter showing the location of the oligonucleotide primer sets, utilized in the ChIP assays. (B) ChIP assay with anti-p53 antibody, anti-acetylated histone H4 antibody or anti-Rad9 antibody for upstream (left) and downstream (right) P21 promoter sites. 293 cells were harvested with or without exposure to UV. ChIP assays were performed using anti-p53 (p53) or anti-acetylated histone H4 antibody (Ac-H4). Anti-c-kit antibody was used as a negative control. (C) ChIP assay for the downstream P21 promoter site. 293 cells were transfected with wild-type or phosphorylation-defective RAD9 plasmids, and harvested before and after exposure to UV. ChIP assays were performed with anti-Rad9 (left) or anti-p53 antibody (right). The relative intensity of signals of immunoprecipitated DNA to input DNA was measured with densitometry. Data represent the means ± SD of three independent experiments. (D) ChIP assay for the upstream P21 promoter site. ChIP assays were performed with anti-Rad9 (left) or anti-p53 antibody (right) for P21 promoter upstream-binding site. Data represent the means ± SD of three independent experiments.