Electron paramagnetic resonance evidence for a C3 ' sugar radical in crystalline d(CTCTCGAGAG) X-irradiated at 4 K

A neutral sugar radical formed by the net loss of hydrogen from C3 ' has be en identified in crystalline DNA X-irradiated at 4 K. Crystals of duplex d( CTCTCGAGAG), known to be of B conformation, were studied using electron par amagnetic resonance (EPR) spectroscopy. The C3 ' radical was identified by using information from dose saturation, power saturation, thermal annealing , and spectrum simulation. The yield of the C3 ' radical, G(C3 '), is 0.03 +/- 0.01 mu mol/J, and its concentration does not appear to saturate up to at least 100 kGy. In the region in which total radical concentration increa ses linearly with dose, the C3 ' radical makes up about 4.5% of the total r adical population trapped in the oligodeoxynucleotide crystal at 4 Ii. Base d on free base release measured in other oligodeoxynucleotides, we suggest that in d(CTCTCGAGAG) the C3 ' radical is responsible for about one-third o f the strand breakage events. (C) 2001 by Radiation Research Society.