title: Sequence context effects on 8-methoxypsoralen photobinding to defined DNA fragments.
abstract: The photoreaction of 8-methoxypsoralen (8-MOP) with DNA fragments of defined sequence was studied. We took advantage of the blockage by bulky adducts of the 3'-5'-exonuclease activity associated with the T4 DNA polymerase. The action of the exonuclease is stopped by biadducts as well as by monoadducts. The termination products were analyzed on sequencing gels. A strong sequence specificity was observed in the DNA photobinding of 8-MOP. The exonuclease terminates its digestion near thymine residues, mainly at potentially cross-linkable sites. There is an increasing reactivity of thymine residues in the order T less than TT much less than TTT in a GC environment. For thymine residues in cross-linkable sites, the reactivity follows the order AT much less than TA approximately TAT much less than ATA less than ATAT less than ATATAA. Repeated A-T sequences are hot spots for the photochemical reaction of 8-MOP with DNA. Both monoadducts and interstrand cross-links are formed preferentially in 5'-TpA sites. Our results highlight the role of the sequence and consequently of the conformation around a potential site in the photobinding of 8-MOP to DNA.
mesh_terms: D000255:Adenosine Triphosphate; D001483:Base Sequence; D055598:Chemical Phenomena; D002621:Chemistry; D004247:DNA / Q000528:radiation effects; D003854:Deoxyribonucleotides; D007700:Kinetics; D008730:Methoxsalen; D010761:Phosphorus Radioisotopes; D014316:Tritium; D014466:Ultraviolet Rays
chemical_list: D003854:Deoxyribonucleotides; D010761:Phosphorus Radioisotopes; D014316:Tritium; D000255:Adenosine Triphosphate; D004247:DNA; D008730:Methoxsalen