title: Highly efficient photochemical 2'-deoxyribonolactone formation at the diagonal loop of a 5-iodouracil-containing antiparallel G-quartet.
abstract: To explore the structure-dependent hydrogen abstraction in antiparallel and parallel G-quartet DNA structures, the photochemical reactivity of 5-iodouracil ((I)U)-containing human telomeric DNA 22-mers was investigated under the 302 nm UV irradiation conditions. We discovered that only antiparallel ODN 4, in which the second T residue in the diagonal loop of the antiparallel G-quartet is substituted with (I)U, was rapidly consumed as compared with parallel ODN 4 and the other (I)U-containing 22-mers under the irradiation conditions. Product analysis of the photolyzate of antiparallel ODN 4 indicated that a 2'-deoxyribonolactone residue was effectively produced at the 5' side of the (I)U residue in the diagonal loop. Photochemical 2'-deoxyribonolactone formation was also found in the (I)U-containing diagonal loop of antiparallel G-quartets d(GGGGTTT(I)UGGGG)(2) and d(GGGGTT(I)UTGGGG)(2), whereas the reaction did not occur at other DNA structures, including the single-stranded form, the loop region of the hairpin, and linear four-stranded G-quartets. The results clearly indicate that this type of 2'-deoxyribonolactone formation efficiently occurrs only in the diagonal loop of the antiparallel G-quartet. Furthermore, we found that 2'-deoxyribonolactone was formed at the (I)U-containing G-rich sequence of the IgG switch regions and the 5' termini of the Rb gene, suggesting the formation of an antiparallel G-quartet with a diagonal loop in these sequences. These results suggest that the present photochemical method can be used as a specific probe for the antiparallel G-quartet with the diagonal loop.
authors.affiliation: Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Chiyoda, Tokyo 101-0062, Japan.
authors.forename: Yan
authors.initials: Y
authors.lastname: Xu
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sugiyama
mesh_terms: D002851:Chromatography, High Pressure Liquid; D007202:Indicators and Reagents; D008027:Light; D008958:Models, Molecular; D008968:Molecular Conformation; D009841:Oligonucleotides / Q000138:chemical synthesis; D010777:Photochemistry; D011188:Potassium / Q000737:chemistry; D012964:Sodium / Q000737:chemistry; D013400:Sugar Acids / Q000737:chemistry*; D013941:Thymine / Q000737:chemistry; D014466:Ultraviolet Rays; D014498:Uracil / Q000031:analogs & derivatives* / Q000737:chemistry*
chemical_list: D007202:Indicators and Reagents; D009841:Oligonucleotides; D013400:Sugar Acids; C056405:2,4,5-trihydroxypentanoic acid gamma-lactone; D014498:Uracil; D012964:Sodium; C048747:5-iodouracil; D013941:Thymine; D011188:Potassium