ヒト細胞中に移入されたX 線照射水和EGFP 発現プラスミド DNA の修復感受性

Clustered DNA damage is defined as two or morelesions (base lesions, single strand breaks or abasic(AP) sites ) localized within one or two helical turn(s).Although repair susceptibility of a synthesized baselesion (or AP) cluster in oligonucleotides have beeninvestigated, those induced actually by irradiation is notclarified yet. To elucidate the repair susceptibility of radiation-induced clustered damage, in the present study,fully hydrated DNA films containing 35 water moleculesper nucleotide, as well as DNA solutions (1×TE, 1μg/μl) were used as samples. In the hydrated DNA films,diffusible water radicals are hardly generated by ionizingradiation. Thus, the major process of radiation actionis direct ionization or impact of secondary electrons toDNA. The EGFP-expressing plasmids were exposedto X-rays with a 1/e dose for each sample, and thentransfected into non-irradiated human cells (MCF-7).Those cells were observed for 48h with fluorescence microscope.DNA repair efficiencies were obtained as thenumber of fluorescence expression cells. The efficiencyfor the hydrated DNA film was significantly lower thanthat for the solution sample. These results indicate thatDNA damage induced in the hydrated DNA would beclustered lesions and difficult to be repaired.日本放射線影響学会第62回大