A COMPARISON OF DNA DAMAGES PRODUCED UNDER CONDITIONS OF DIRECT AND INDIRECT ACTION OF RADIATION

Studies using a P-32-postlabelling assay reveal that at both low and h igh concentrations of hydroxyl radical scavenger, DNA damage from alph a-irradiation is similar to that from gamma-irradiation. At low concen trations of scavenger the identified damages are predominantly thymine glycol (T-g) and phosphoglycolate (pg) lesions, indicative of indirec t hydroxyl radical ( OH) action. However, at high concentrations of sc avenger (i.e. where direct effects are expected to dominate) a somewha t different pattern of damage is observed after alpha- and gamma-irrad iation, with several novel lesions detected. Further experiments, in w hich the results of DMSO scavenging of irradiated DNA solutions are co mpared with glycerol scavenging and irradiation of 'dry' solid DNA, de monstrate that both direct effects and scavenger-derived secondary rad icals contribute to the different spectra of lesions observed upon irr adiation of highly scavenged DNA systems. Generally, irradiation under conditions that favour direct damage result in a lower relative yield of pg, whilst for the highly scavenged systems T-g damages persist. T o account for this we propose that T-g are efficiently produced by dir ect action in these systems. Differences seen upon irradiation of the 'dry' system, compared with those of dilute aqueous solution, suggest that direct action yields a distinct spectrum of lesions.