STRAND BREAKS IN PLASMID DNA FOLLOWING POSITIONAL CHANGES OF AUGER-ELECTRON-EMITTING RADIONUCLIDES

The purpose of our studies is to elucidate the kinetics of DNA strand breaks caused by low-energy Auger electron emitters inclose proximity to DNA. Previously we have studied the DNA break yields in plasmids af ter the decay of indium-lll bound to DNA or free in solution. In this work, we compare the DNA break yields in supercoiled DNA of iodine-125 decaying close to DNA following DNA intercalation, minor-groove bindi ng, or surface binding, and at a distance from DNA. Supercoiled DNA, s tored at 4 degrees C to accumulate radiation dose from the decay of I- 125, was then resolved by gel electrophoresis into supercoiled, nicked circular, and linear forms, representing undamaged DNA, single-strand breaks, and double-strand breaks respectively. DNA-intercalated or gr oove-bound I-125 is more effective than surface-bound radionuclide or I-125 free in solution. The hydroxyl radical scavenger DMSO protects a gainst damage by I-125 free in solution but has minimal effect on dama ge by groove-bound I-125.