THE ACTION SPECTRUM (313–435 nm) FOR KILLING HOECHST 33258 TREATED CHINESE HAMSTER OVARY CELLS CONTAINING BROMODEOXYURIDINE SUBSTITUTED DNA

Abstract— The action spectrum (313–435 nm) for killing Chinese hamster ovary cells containing bromo‐deoxyuridine substituted DNA and treated with Hoechst 33258 was very similar to the absorption spectrum of the dye bound to chromatin, indicating that sensitization was mediated through direct absorption of radiation by the dye. The ratio of sensitization cross sections for 365 nm (plus dye) to 313 nm (no dye) was approx. 30 while this ratio for strand breakage was about one. These results are in agreement with the hypothesis that strand breaks are not the major class of lethal photoproducts induced via Hoechst 33258 sensitization.