title: Contrasting structural impacts induced by cis-syn cyclobutane dimer and (6-4) adduct in DNA duplex decamers: implication in mutagenesis and repair activity.
abstract: The relative biological importance of cis--syn cyclobutane dimer and pyrimidine(6-4)pyrimidone photoadduct ([6-4] photoadduct) appears to be dependent on the biological species, dipyrimidine sites and local conformational variation induced at the damaged sites. The single-strained deoxynucleotide 10-mers containing the site-specific (6-4) adduct or cis--syn cyclobutane dimer of thymidylyl(3'-->5')-thymidine were generated by direct photolysis of d(CGCATTACGC) with UVC (220-260 nm) irradiation or UVB (260-320 nm) photosensitization. Three-dimensional structures of the duplex cis--syn and (6-4) decamers of d(CGCATTACGC)xd(GCGTAATGCG) were determined by NMR spectroscopy and the relaxation matrix refinement method. The NMR data and structural calculations establish that Watson-Crick base pairing is still intact at the cis--syn dimer site while the hydrogen bonding is absent at the 3'-side of the (6-4) lesion where the T-->C transition mutation is predominantly targeted. Overall conformation of the duplex cis--syn decamer was B-DNA and produced a 9 degree bending in the DNA helix, but a distinctive base orientation of the (6-4) lesion provided a structural basis leading to 44 degree helical bending. The observed local structure and conformational rigidity at the (6-4) adduct of the thymidylyl(3'-5')-thymidine (T-T [6-4]) lesion site suggest the potential absence of hydrogen bonding at the 3' sides of the (6-4) lesion with a substituted nucleotide during replication under SOS conditions. Contrasting structural distortions induced ny the T-T (6-4) adduct with respect to the T-T cis--syn cyclobutane pyrimidine photodimer may explain the large differences in mutation spectrum and repair activities between them.
authors.affiliation: Department of Chemistry, Korea Advanced Institute of Science and Technology, Taejon.
authors.forename: J K
authors.initials: JK
authors.lastname: Kim
authors.forename: D
authors.initials: D
authors.lastname: Patel
authors.forename: B S
authors.initials: BS
authors.lastname: Choi
mesh_terms: D001483:Base Sequence; D018736:DNA Adducts; D004260:DNA Repair; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D015394:Molecular Structure; D016296:Mutagenesis; D009690:Nucleic Acid Conformation; D011740:Pyrimidine Dimers / Q000737:chemistry*
chemical_list: D018736:DNA Adducts; D011740:Pyrimidine Dimers