Photo-Induced DNA Double-Strand Breaks Monitored by Single-Molecule Observation: Protective Effect of Antioxidative Compounds

We have performed a real-time observation of photo-induced breakage on individual long DNA molecules stained by a cyanine dye, YOYO, under the intense illumination in solution. It is known that YOYO has ability to photo-cleave probed DNA by generating reactive oxygen species. We analyzed the kinetics of the breakage reaction in a quantitative manner. It was found that the breakage reaction is protected by antioxidative compounds; ascorbic acid and a water-soluble flavonoid, glucosyl-rutin. To interpret the kinetic process of the double-strand breakage reaction, a two-step mechanism is proposed.