Oxygen free radical damage to DNA. Translesion synthesis by human DNA polymerase eta and resistance to exonuclease action at cyclopurine deoxynucleoside residues

J Biol Chem. 2001 Dec 28;276(52):49283-8. doi: 10.1074/jbc.M107779200. Epub 2001 Oct 24.


Cyclopurine deoxynucleosides are common DNA lesions generated by exposure to reactive oxygen species under hypoxic conditions. The S and R diastereoisomers of cyclodeoxyadenosine on DNA were investigated separately for their ability to block 3' to 5' exonucleases. The mammalian DNA-editing enzyme DNase III (TREX1) was blocked by both diastereoisomers, whereas only the S diastereoisomer was highly efficient in preventing digestion by the exonuclease function of T4 DNA polymerase. Digestion in both cases was frequently blocked one residue before the modified base. Oligodeoxyribonucleotides containing a cyclodeoxyadenosine residue were further employed as templates for synthesis by human DNA polymerase eta (pol eta). pol eta could catalyze translesion synthesis on the R diastereoisomer of cyclodeoxyadenosine. On the S diastereoisomer, pol eta could catalyze the incorporation of one nucleotide opposite the lesion but could not continue elongation. Although pol eta preferentially incorporated dAMP opposite the R diastereoisomer, elongation continued only when dTMP was incorporated, suggesting bypass of this lesion by pol eta with reasonable fidelity. With the S diastereoisomer, pol eta mainly incorporated dAMP or dTMP opposite the lesion but could not elongate even after incorporating a correct nucleotide. These data suggest that the S diastereoisomer may be a more cytotoxic DNA lesion than the R diastereoisomer.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • DNA Damage*
  • DNA Repair
  • DNA Replication / genetics
  • DNA-Directed DNA Polymerase / metabolism*
  • Exonucleases / metabolism*
  • Free Radicals
  • Humans
  • Models, Molecular
  • Molecular Structure
  • Oligonucleotides / chemistry*
  • Oligonucleotides / metabolism
  • Reactive Oxygen Species / metabolism*


  • Free Radicals
  • Oligonucleotides
  • Reactive Oxygen Species
  • DNA-Directed DNA Polymerase
  • Rad30 protein
  • Exonucleases