title: Photoreaction at 5'-(G/C)AA(Br)UT-3' sequence in duplex DNA: efficient generation of uracil-5-yl radical by charge transfer.
abstract: The photoreactivities of 5-halouracil-containing DNA have widely been used for analysis of protein-DNA interactions and have recently been used for probing charge-transfer processes along DNA. Despite such practical usefulness, the detailed mechanisms of the photochemistry of 5-halouracil-containing DNA are not well understood. We recently discovered that photoirradiation of BrU-substituted DNA efficiently produced 2'-deoxyribonolactone at 5'-(G/C)AABrUBrU-3' and 5'-(G/C)ABrUBrU-3' sequences in duplex DNA. Using synthetic oligonucleotides, we found that similar photoreactivities were maintained at the 5'-(G/C)AABrUT-3' sequence, providing ribonolactone as a major product with concomitant release of adenine base. In this paper, the photoreactivities of various oligonucleotides possessing the 5'-BrUT-3' sequence were examined to elucidate the essential factors of this photoreaction. HPLC product analysis indicated that the yield of 2'-deoxyribonolactone largely depends on the ionization potential of the purine derivatives located 5'-upstream of 5'-BrUT-3', as well as the electron-donating ability of their pairing cytosine derivatives. Oligonucleotides that possess G in the complementary strand provided the ribonolactone with almost the same efficiency. These results clearly suggest that the photoinduced charge transfer from the G-5' upstream of 5'-BrUT-3' sequence, in the same strand and the complementary strand, initiates the reaction. To examine the role of intervening A/T base pair(s) between the G/C and the 5'-BrUT-3' sequence, the photoreactivities of a series of oligonucleotides with different numbers of intervening A/T base pairs were examined. The results revealed that the hotspot sequence consists of the electron-donating G/C base pair, the 5'-BrUT-3' sequence as an acceptor, and an appropriate number of A/T base pairs as a bridge for the charge-transfer process.
authors.affiliation: Division of Biofunctional Molecules, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, 2-3-10 Surugadai, Kanda, Chiyoda, Tokyo, Japan.
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Ryu
authors.initials: R
authors.lastname: Tashiro
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sugiyama
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000737:chemistry; D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D006147:Guanine / Q000737:chemistry; D008027:Light; D008958:Models, Molecular; D010777:Photochemistry; D011687:Purines / Q000737:chemistry; D014498:Uracil / Q000737:chemistry*
chemical_list: D011687:Purines; D014498:Uracil; D006147:Guanine; D004247:DNA; D000225:Adenine