Abstract
Double-strand breaks (DSBs) in the DNA are a major threat for all of the living cells on the earth. Because of the biological significance, there have appeared many studies to try to measure DSBs. However, it is known that, by use of usual biochemical methodologies, quantitative evaluation is applicable only for high dose conditions. We have currently been developing the experimental method of single DNA observation on giant DNA molecules with fluorescence measurement. By applying single DNA observation, it has become possible to evaluate the probability of DSBs down to the low probability on the order of one breakage per several hundreds kbp. Actually, we have demonstrated that the DSBs induced by active oxygen species generated by photon are highly suppressed by the addition of polyamine, where the effect of polyamine is not to diminish the active oxygen species but to collapse the giant DNA into a compact state.
In the present paper, as the extension of this methodology we report the result of quantitative evaluation of DSBs induced by gamma-ray. It is demonstrated that the probability of DSBs per base pair is proportional to gamma-ray radiation dose (less than 100Gy) and that 1.7 DSBs are induced by 1Gy radiation dose per 10Mbp, which corresponds to one DSB per single human cell by 1mGy dose. Next challenge is the evaluation on the DSBs for the condensed human genomic DNA molecules caused by gamma-ray.
