Figure 2.

Double-strand breaks detected by PFGE in response to BrdU photolysis and IR. (A) Autoradiogram showing the extent of DNA released after BrdU photolysis and IR. U87 cells were exposed to a UV-A dose of 1,500 J/m²; without BrdU (Lanes 1–6), with BrdU (lanes 7–12) and collected at 0.5, 1, 3, 6 and 24 h or U87 cells were exposed to 10, 20 and 40 Gy of IR (lanes 13–15) and collected immediately. (B and C) Densitometic analysis of (A) presented in graph form. (B) Data points, DNA released from lanes 1–12 plotted over time. (C) Data points, DNA released from lanes 13–15 plotted against IR dose. (D) UV-A dose response of DSBs from BrdU photolysis at 1 h. Data points, fraction of DNA released plotted against the indicated UV-A doses. The intercept of the dotted lines indicates the minimum UV-A dose resulting in DSBs detected by PFGE. Using the graphs in (C) and (D) and assuming a linear relationship between DSBs and IR and UV-A dose, respectively, the Gy equivalent doses for 150, 500 and 1,500 J/m² of UV-A corresponds to 2, 5, 6 and 18–20 Gy, respectively.