title: Origin of the heterogeneous distribution of the yield of guanyl radical in UV laser photolyzed DNA.
abstract: Oxidative guanine lesions were analyzed, at the nucleotide level, within DNA exposed to nanosecond ultraviolet (266 nm) laser pulses of variable intensity (0.002-0.1 J/cm(2)). 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 and single-stranded oligomer DNA at a size of 33-37 nucleobases. Lesions were analyzed 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 pi-stack, it can be assessed that the distance range of migration is <6-8 bp.
authors.affiliation: UMR 8113 French National Center for Scientific Research, Institut Gustave Roussy, 94805 Villejuif, France.
authors.forename: Dimitar
authors.initials: D
authors.lastname: Angelov
authors.forename: Benedicte
authors.initials: B
authors.lastname: Beylot
authors.forename: Annick
authors.initials: A
authors.lastname: Spassky
mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine; D001483:Base Sequence; D055592:Biophysical Phenomena; D001703:Biophysics; D002412:Cations; D004247:DNA / Q000737:chemistry / Q000528:radiation effects* / Q000648:ultrastructure; D043382:DNA-Formamidopyrimidine Glycosylase / Q000737:chemistry; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000737:chemistry; D019281:Dimerization; D004492:Edetic Acid / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D005609:Free Radicals / Q000737:chemistry*; D006147:Guanine / Q000737:chemistry*; D007477:Ions; D007834:Lasers; D008956:Models, Chemical; D015233:Models, Statistical; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000737:chemistry; D010081:Oxazolone / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D010782:Photolysis; D017785:Photons; D010880:Piperidines / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011740:Pyrimidine Dimers / Q000737:chemistry; D012313:RNA / Q000737:chemistry; D013053:Spectrophotometry; D013696:Temperature; D014466:Ultraviolet Rays
chemical_list: D002412:Cations; D005609:Free Radicals; D007477:Ions; D009841:Oligonucleotides; D010880:Piperidines; D011108:Polymers; D011740:Pyrimidine Dimers; D010081:Oxazolone; D006147:Guanine; D012313:RNA; C032727:piperidine; D000080242:8-Hydroxy-2'-Deoxyguanosine; D004247:DNA; D004492:Edetic Acid; D043382:DNA-Formamidopyrimidine Glycosylase; D003849:Deoxyguanosine; D010100:Oxygen