Low-energy electrons inside active DNA models: a tool to elucidate the radiation action mechanisms.

To postulate radiation action mechanisms and to test them by Monte Carlo simulation, a complex computer model was developed consisting of major components for the generation of a radiation spectrum, biomolecular structures, and electron track structures in liquid water. As the radiation source 125I is employed here; it is an excellent test radiation due to its exactly localized position in the DNA molecule and high biological toxicity as a consequence of the emission of short-ranging Auger electrons. A linear DNA plasmid model (Pomplun 1991) which can actively respond to radical attack (Terrissol and Pomplun 1994) has been modified into a nucleosome model representing the double-helix of DNA with 146 basepairs and more than 9000 atoms surrounding the histones. The introduction of this new target structure allows a more realistic simulation of cellular conditions. Using the model's decay accumulation aspect, the situation of many break and survival experiments can be approximated and the influence of several cellular parameters tested. As a first step, a correlation between the size of energy depositions and strand-break patterns was sought.