Base Liberation and Concomitant Reactions in Irradiated DNA Solutions

Abstract

Irradiation of aqueous solutions of DNA causes liberation of free nucleobases and of compounds which behave chromatographically like nucleosides. These components can be separated from irradiated DNA by DEAE-Sephadex chromatography. Their amount increases linearly with dose, resulting in a G-value of 0'16 to 0·18. Further separation of the liberated products by ion-exchange chromatography on Dowex 50 x4 and by thin-layer chromatography on cellulose plates shows that about 60 per cent of the liberated material consists of nucleosides, part of which carries a damaged sugar molecule. Different methods used to determine the formation of malonic dialdehyde in irradiated DNA lead to the conclusion that this type of sugar damage does not contribute very much to the breakage of the DNA backbone. Several mechanisms leading to single strand breaks in DNAare discussed.

Specificity of ionizing radiation–induced mutagenesis in thelacregion of single–stranded phage M13 mp10 DNA

“…Similar preferential incorporation of dAMP in vivo have been reported for heat-induced apurinic sites (14) and for neocarzinostatin-induced apyrimidinic sites at cytosine residues of lambda cI mutants (24). The formation of AP sites by ionizing radiation has been already established, e.g., 0.06 base released per 100 eV (25). Our finding that dAMP is most preferentially incorporated opposite the damaged nucleotide suggests that AP site formation also play a role in ionizingradiation mutagenesis.…”

Studies on the Radiosensitizing Effect of Oxygen in Chinese Hamster Cells

“…This radiation chemical model emphasizes the quantitative difference in DNA strand breakage produced under conditions of oxygenation and hypoxia . It is also known that there is a qualitative difference in the chemistry of DNA breaks generated under oxygenated or hypoxic conditions (Kapp and Smith 1970, Ullrich and Hagen 1971) . It was this difference, among other factors, which led Town, Smith and Kaplan (1973) to postulate an ' ultrafast enzymic repair ', selective for DNA damage generated in hypoxia, to account for the oxygen effect in bacterial cells .…”

Mechanisms of induction and repair of DNA double-strand breaks by ionizing radiation: Some contradictions

“…A variety of base alterations have been detected by chemical and immunological methods (West et al 1982a, b;Teoule 1987;Chen et al 1990;Dizdaroglu 1992). There is also a release of intact bases from the nucleotide strand (Ullrich and Hagen 1971) and of modified sugars (von Sonntag 1987).…”