Figure 6.

Chk1 phosphorylation by ATR in G1 phase occurs in the absence of RPA2 phosphorylation and is independent of transcription. (A) Immunoblots of synchronized U2OS irradiated in G1 phase with 2 Gy and/or treated with ETP-46464 for 1 h (+15 to +75 min following IR). (B) Immunoblots of synchronized U2OS following 2 Gy and/or inhibition of transcription or BER. Synchronized U2OS cells in G1 were treated for 1 h with an inhibitor of RNA polymerases II and III (α-amanitin) or of APE1 (NSC332395) before exposure to 2 Gy IR. Inhibitors were not taken off and cells were harvested 1 h after IR. 127 × 122 mm (300 × 300 DPI).