Radiation sensitivity of transforming DNA.

Biologically active DNA isolated from Bacillus subtilis was exposed in vitro to X-rays at a concentration of 10 microgram/ml in 29 mM phosphate buffer. Radiation-induced damage to the DNA was quantitatively determined by measuring the decrease in its transforming activity (try2 locus) using B. subtilis 168M (try-) as recipient. In O2, which removes .H and eaq-, the radiation sensitivity of the DNA is less than that in N2-saturated water. In N2O, which has been shown to increase yields of .OH in irardiated aqueous solutions, the radiation sensitivity of Transforming DNA is twice that observed in O2 and 1.5 times that in N2. Addition of 5 X 10(-2) M ethanol or 1.7 X 10(-1) M t-butanol, both .OH scavengers, causes large (about tenfold) reduction in the radiation sensitivity in all three saturating gases. These results suggest the importance of the .OH radical in the loss of biological activity of DNA.