Oxygen Effect In Gamma-Irradiated Dna

Summary DNA from bacteriophage T1 or calf thymus DNA wasγ-irradiated in dilute solution at 200 µg/ml in absence and in presence of oxygen. A variety of physico-chemical and biological properties was measured and the respective oxygen enhancement ratios (o.e.r.) were calculated. For the occurrence of single and double strand breaks, formation of terminal phosphate end groups and for the base damage o.e.r.-values between 2 to 4 are measured. Whereas the formation of ‘actual’ breaks results to an o.e.r. of 1.8, the induction of alkalilabile lesions in the nucleotide strand seems to occur rather exclusively in presence of oxygen. In contrast to physico-chemical alterations, the inactivation of biological functions does not show any oxygen effect as determined by the priming activity of thymus DNA with respect to enzymatic RNA synthesis or by the infectivity of T1-DNA in a spheroplast system withE. coli hcr+ (K12) or hcr− (K12 A16). The discrepancy between the o.e.r. for biological inactivation and that for the structural damage in DNA is discussed.