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

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