ORIGIN OF THE HETEROGENOUS DISTRIBUTION OF THE YIELD OF
GUANYL RADICAL IN UV LASER PHOTOLYSED DNA
Dimitar Angelov 1, Benedicte Beylot 2 and Annick Spassky 3*
1 bulgarian academy of sciences
2 paris6 university
3 cnrs
* To whom correspondence should be addressed. E-mail: aspassky{at}igr.fr.
Submitted on July 8, 2004
Revised on August 18, 2004
Accepted on 6 December 2004
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Abstract |
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Oxidative guanine lesions were analysed, at the nucleotide level, within DNA exposed to nanosecond UV (266 nm) laser pulses of variable intensity (0.002 to 0.1 J/cm2). Experiments were carried out, at room temperature, in TE buffer (20 mM Tris-HCl, pH 7.5; 1 mM EDTA) containing 35 mM NaCl, on 5'-end radioactively labeled double stranded (ds) and single stranded (ss) oligomer DNA at a size of 33 to 37 nucleobases. Lesions were analysed on polyacrylamide gel electrophoresis by taking advantage of the specific removal of 8-oxodG from DNA by the formamidopyrimidine DNA glycosylase (Fpg protein) and of the differential sensitivity of 8-oxodG and oxazolone to piperidine. The quantum yields of lesions at individual sites, determined from the normalized intensities of bands, were plotted against the irradiation energy levels. Simplified model fitting of the experimental data enabled to evaluate the spectroscopic parameters characterizing excitation and photoionization processes. Results show that the distribution of guanine residues, excited to the lowest triplet state or photoionized, is heterogeneous and depends on the primary and secondary DNA structure. These findings are generalized in terms of excitation energy and charge migration mediated biphotonic ionization. On the basis of the changes in the yield of the guanyl radical resulting from local helical perturbations in the DNA 
-stack, it can be assessed that the distance range of migration is less than 6-8 bp.
Key Words:
BIPHOTONIC IONIZATION, DNA ENERGY AND CHARGE MIGRATION, DNA OXIDATIVE DAMAGE, UV BIPHOTONIC CHEMISTRY, UV LASER PHOTOFOOTPRINTING
