Sequence context effects on 8-methoxypsoralen photobinding to defined DNA fragments

Biochemistry. 1987 Jun 16;26(12):3307-14. doi: 10.1021/bi00386a010.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate
  • Base Sequence
  • Chemical Phenomena
  • Chemistry
  • DNA* / radiation effects
  • Deoxyribonucleotides
  • Kinetics
  • Methoxsalen*
  • Phosphorus Radioisotopes
  • Tritium
  • Ultraviolet Rays

Substances

  • Deoxyribonucleotides
  • Phosphorus Radioisotopes
  • Tritium
  • Adenosine Triphosphate
  • DNA
  • Methoxsalen