title: Structure of the DNA interstrand cross-link of 4,5',8-trimethylpsoralen.
abstract: 4,5',8-Trimethylpsoralen (TMP) cross-links a 5' TpA or a 5' ApT site by photoreacting with one thymine moiety in each DNA strand. We are interested in whether psoralen interstrand cross-links all share one structure or whether there are significant differences. In this paper, we employed a rapid method for probing the structure of the cross-link by making a series of TMP cross-linked duplexes containing specific base-pair mismatches. The relative stability provided by a base pair can be correlated with neighboring base pairs by comparing the extents of gel retardation when base-pair mismatches happen in each position. From our studies, we infer that with respect to the furan-side strand, the 5'T.A base pair of the two T.A base pairs in the TpA site is not hydrogen bonded. Immediately on each side of the cross-linked TpA site is a highly stabilized base pair. Next, a region of decreased stability occurs in each arm of a cross-linked duplex and these base pairs of least stability are located farther away from the cross-linked thymines as the lengths of the arms of the cross-linked helix increase. Finally, even in 7 M urea at 49 degrees C the cross-linked helix is hydrogen bonded at both ends of a duplex of 22 base pairs. We propose that the structures of interstrand cross-links in DNA vary appreciably with the DNA sequence, the length of the DNA duplex, and the structures of the DNA cross-linking agents.
authors.affiliation: Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111.
authors.forename: K R
authors.initials: KR
authors.lastname: Kumaresan
authors.forename: M
authors.initials: M
authors.lastname: Ramaswamy
authors.forename: A T
authors.initials: AT
authors.lastname: Yeung
mesh_terms: D001482:Base Composition; D001483:Base Sequence; D003432:Cross-Linking Reagents / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D004591:Electrophoresis, Polyacrylamide Gel; D006860:Hydrogen Bonding; D008961:Models, Structural; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000138:chemical synthesis / Q000737:chemistry*; D013329:Structure-Activity Relationship; D013941:Thymine; D014307:Trioxsalen / Q000737:chemistry*
chemical_list: D003432:Cross-Linking Reagents; D009838:Oligodeoxyribonucleotides; D004247:DNA; D013941:Thymine; D014307:Trioxsalen