Base Liberation and Concomitant Reactions in Irradiated DNA Solutions

Abstract

SummaryIrradiation 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 × 4 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 DNA are discussed.