PHOTOCHEMICAL PRODUCTION OF DOUBLE-STRAND BREAKS IN CELLULAR DNA

In a recent publication we described a novel route for the introductio n of DNA double-strand breaks (DSBs) into cellular DNA. This involved the labelling of cellular DNA with bromodeoxyuridine (BrdU) and exposu re to UVA light in the presence of Hoechst dye No. 33258, Here, we rep ort an extension of that work to the use of iododeoxyuridine (IdU); ce lls substituted with known levels of IdU were subjected to a similar p hotolysis 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. T he 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 simi lar to 15-fold less SSBs and 5-fold less DSBs are produced per IdU tha n per BrdU moiety.