Clustered DNA damages induced by low-energy (1~20 eV) electrons and the general mechanism of transient anions

Abstract

Five monolayer plasmid DNA films were irradiated by low-energy electrons (LEEs) (1~20 eV) in ultra-high vacuum. Crosslinks, single-strand breaks, double-strand breaks and the loss of the supercoiled configuration were analyzed via agarose gel electrophoresis. Base damages were revealed by Escherichia coli base excision and repair endonucleases (Nth and Fpg). The electron energy dependence for the effective yields of various DNA damages showed that no clustered damage within 20 base pairs could be caused by electrons <4 eV. Crosslinks, SSBs, base damage-related crosslinks, and isolated base modifications had maxima at 5 eV and 10 eV, while the peak of DSB and non-DSB clustered damage occurred at 6 eV and 10 eV. These maxima are ascribed to core-excited resonances, which decay into bond-breaking channels leading to DNA damages. The mechanism of DNA clustered damage induced by a single LEE is elucidated through the process of the formation of transient anions and the subsequent electron transfer.

Keywords

• dna
• clustered damage
• low-energy electrons
• transient anions
• ionizing radiation