Quantitative analysis of double-strand break in giant DNA by single-molecule observation

We have performed a real-time observation of photo-induced double-strand breaks of giant DNAs stained by a cyanine dye, YOYO, under intense illumination in solution using fluorescence microscopy. YOYO is known to have the ability to photo-cleave DNAs by generating reactive oxygen species such as hydroxyl radicals. We have also investigated the effect of antioxidants such as a water-solubule flavonoid, glucosyl-hesperidin, and ascorbic acid (vitamin Q on preventing double-strand breaks in a quantitative manner. It is stressed that the experimental methodology of single chain observation serves as a useful tool for studying the double-strand break of giant DNA.