MONTE-CARLO SIMULATION OF DNA STRAND BREAK INDUCTION IN SUPERCOILED PLASMID PBR322 DNA FROM INDIRECT EFFECTS

We present a new Monte Carlo simulation code system (DBREAK) of the de tailed events that occur when ionizing radiation interacts with water and DNA molecules. The model treats the initial energy deposition by r adiation, the formation of chemically active species, subsequent diffu sion-controlled chemical reactions, and induction of DNA strand breaks . DBREAK assumes one-hit single-strand break (SSB) and two-hit double- strand break (DSB) mechanisms. A high-resolution model of plasmid DNA structure has been introduced. The calculated results are compared wit h the results of previously performed experiments of the same type. Un der aerobic conditions, 89.4% of the DNA damage was attributed to OH-r adical and 10.5% and 0.1% to e(aq)(-) and H, respectively. We also com pared the differences between liquid-water track structure and gas-pha se-water track structure. The calculated yield of SSBs by liquid-water track structure exceeded that of gas-phase-water track structure by a factor of 1.2.