MEASUREMENT OF DNA-DAMAGE BY ELECTRONS WITH ENERGIES BETWEEN 25 AND 4000 EV

All ionizing radiations deposit energy stochastically along their trac ks. The resulting distribution of energies deposited in a small target such as the DNA helix leads to a corresponding spectrum in the severi ty of damage produced. So far, most information about the probable spe ctra of DNA lesion complexity has come from Monte Carlo studies which endeavour to model the relationship between the energy deposited in DN A and the damage induced. The aim of this paper is to establish method s of determining this relationship by irradiating pBR322 plasmid DNA u sing low energy electrons with energies comparable with the minimum en ergy thought to produce critical damage. The technique of agarose gel electrophoresis has been used to ascertain the fraction of DNA single- and double-strand breaks induced by monoenergetic electrons with ener gies as low as 25 eV. Our data show that the threshold electron energy for induction of single-strand breaks is < 25 eV, and for double-stra nd breaks between 25 and 50 eV.