Photochemical production of double-strand breaks in cellular DNA

In a recent publication we described a novel route for the introduction of DNA double-strand breaks (DSBs) into cellular DNA. This involved the labelling of cellular DNA with bromodeoxyuridine (BrdU) and exposure to UVA light in the presence of Hoechst dye No. 33258. Here, we report an extension of that work to the use of iododeoxyuridine (IdU); cells substituted with known levels of IdU were subjected to a similar photolysis treatment and analyzed for strand breaks by elution assays. Results indicate that both single-strand breaks (SSBs) and DSBs depend linearly on the level of IdU substitution and fluence of UVA light. The yields of SSBs and DSBs were found to be 3.5 x 10(-5) and 9.5 x 10(-7)/IdU moiety/kJm-2, respectively. These results indicate that approximately 15-fold less SSBs and 5-fold less DSBs are produced per IdU than per BrdU moiety.