(A) RPA2 hyperphosphorylation induced by UV irradiation is dependent on DNA-PK. Expression of ATR, ATM, DNA-PK, TEL2, or CHK1 were silenced by siRNA in HEK293T cells and RPA2 hyperphosphorylation in response to 60 J/m2 UV irradiation was monitored. (B) RPA2 hyperphosphorylation is also dependent on the DNA binding subunit of DNA-PK, Ku86. (C) DNA-PKcs-null HCT116 cells do not express DNA-PKcs. (D) DNA-PKcs-null (DNA-PK−/−) HCT116 cells do not show RPA2 hyperphosphorylation in response to UV irradiation or 4NQO treatment compared to the parental HCT116 cells (DNA-PK+/+). (E) DNA-PK−/− (MO59J) cells do not express ATM and DNA-PK. (F) DNA-PK−/− (MO59J) cells do not show RPA2 hyperphosphorylation in response to 4NQO treatment compared to a matched DNA-PK+/+ (MO59K) cell line. (G) Lymphocytes defective in ATR (Seckel) or ATM (ATM−/−) as well as wild type lymphocytes produce RPA2 hyperphosphorylation in response to 4NQO treatment. Hyperphosphorylation, intermediate phosphorylation, and no phosphorylation of RPA2 are indicated as H, M, and B, respectively. NC, non-targeting control siRNA.