Guanine is the target for direct ionisation damage in DNA, as detected using excision enzymes.
Exposure of an aqueous, aerated solution (pH 7) of a double-stranded DNA to 193 nm light, of sufficient energy to ionise DNA, leads to selective, non-random modification at guanine in the form of frank single-strand break (ssb) and base modifications, revealed by treatment with either Escherichia coli formamidopyrimidine-DNA glycosylase (Fpg), Escherichia coli endonuclease III (Nth) or hot piperidine treatment. There is a similar neighbouring base sequence dependence for Fpg- and Nth-sensitive damage as that previously reported for both hot alkali-labile damage and prompt ssb. Low yields of photoproducts, namely pyrimidine dimers, are also revealed using the enzyme T4 endonuclease V (T4 endo V). Although irradiation of DNA with 193 nm light causes photoionisation of all the nucleic acid bases, these results indicate that guanine is the predominant site for localisation of the oxidative damage. These findings are consistent with migration of the radical cation to 'target' damage at guanine sites.
MRC Radiation and Genome Stability Unit, Harwell, OX11 ORD, UK. melvin@cnrs-orleans.fr
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Cunniffe
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O'Neill
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Parker
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Roldan-Arjona
D001483:Base Sequence; D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects*; D004249:DNA Damage; D043382:DNA-Formamidopyrimidine Glycosylase; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004706:Endodeoxyribonucleases; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins; D006147:Guanine / Q000737:chemistry* / Q000528:radiation effects*; D007477:Ions; D008027:Light; D008969:Molecular Sequence Data; D009699:N-Glycosyl Hydrolases; D010084:Oxidation-Reduction; D010777:Photochemistry; D010957:Plasmids / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects; D011740:Pyrimidine Dimers / Q000737:chemistry / Q000528:radiation effects
D029968:Escherichia coli Proteins; D007477:Ions; D011740:Pyrimidine Dimers; D006147:Guanine; D004247:DNA; D004706:Endodeoxyribonucleases; D043224:Deoxyribonuclease (Pyrimidine Dimer); C106403:NTH protein, E coli; D009699:N-Glycosyl Hydrolases; D043382:DNA-Formamidopyrimidine Glycosylase; C468610:DNA-formamidopyrimidine glycosylase, E coli