Fig. 4.

TopBP1-dependent stimulation of ATR kinase activity by N-Aco-AAF-damaged DNA. (A) (Upper) Kinase assays were performed with 85 mM final salt concentration as described in the legend of Fig. 3, except with 0.62–5 nM unmodified (UM) or N-Aco-AAF-damaged (AAF) pUC19 plasmid DNA. (Lower) The average levels of Chk1 phosphorylation from four independent experiments are quantitated in the graph. (B) (Upper) Time course of Chk1 phosphorylation. Kinase assays as in A were carried out with 0.62 nM DNA for the times indicated. (Lower) The average levels of Chk1 phosphorylation from two independent experiments are quantitated in the graph.