Influence of heavy ions on the transforming activity of DNA

Changes in functional activity following treatment of DNA with heavy ions were analysed by transformation assay. Biological response to exposure to charged particles, 10B, 12C, and 22Ne, was evaluated by the extent of inactivation of ability of DNA to transfer the genetic marker of tryptophane independence. The possibility of protecting the biological activity of DNA was studied using a conventional protector, cysteamine hydrochloride, or the preparation cytriphos, synthesized at the Institute of Radiobiology and Radiation Hygiene, Sofia. Dried samples of donor DNA isolated from a Bacillus subtilis prototroph strain were exposed to doses of 50 krad to 1 Mrad. For the three types of charged particles used, dose response of the inactivation process was defined by an exponential function. Comparison of response curves for the three types of radiation showed the effect to be dependent on LET, being highest for 10B and lowest for 22Ne. In all three cases, addition of a protective substance failed to produce any change in the biological effect observed.