DNA Protection against Damages Induced by Low-Energy Electrons: Absolute Cross Sections for Arginine-DNA Complexes.

Histone proteins protect cellular DNA from radiation damage. We find that arginine, a major component of histone proteins, protects DNA from lesions induced by low-energy secondary electrons generated by radiation. Thin films of 7 ± 2, 12 ± 4, and 17 ± 4 nm thicknesses containing arginine-plasmid-DNA complexes in molar ratio of [Arg 2+ ]/[PO 4 - ] = 16 are irradiated in vacuum with 5 and 10 eV electrons. Damage yields are measured for base damages, cross-links, single-strand breaks (SSBs), double-strand breaks, and other clustered lesions. Most damage results from dissociative electron attachment. Absolute cross sections (ACSs) for all damage types are extracted from yields at different film thicknesses. Compared with bare DNA, these ACSs are reduced by factors of up to 4.4 in Arg-DNA complexes. SSB protection is the highest. Potentially lethal cluster lesions decrease by factors of up to 2.2. ACSs are critical input parameters in modeling radiation-induced damage and assessing protection factors under simulated cellular conditions.