Human DNA polymerase N (POLN) is a low fidelity enzyme capable of error-free bypass of 5S-thymine glycol

J Biol Chem. 2006 Aug 18;281(33):23445-55. doi: 10.1074/jbc.M604317200. Epub 2006 Jun 19.


Human DNA polymerase N (POLN or pol nu) is the most recently discovered nuclear DNA polymerase in the human genome. It is an A-family DNA polymerase related to Escherichia coli pol I, human POLQ, and Drosophila Mus308. We report the first purification of the recombinant enzyme and examination of its biochemical properties, as a step toward understanding the functions of POLN. Unusual for an A-family DNA polymerase, POLN is a low fidelity enzyme incorporating T opposite template G with a frequency of 0.45 and G opposite template T with a frequency of 0.021. The frequency of misincorporation of T opposite template G is higher than any other known DNA polymerase. POLN has a processivity of DNA synthesis (1-100 nucleotides) similar to the exonuclease-deficient Klenow fragment of E. coli pol I, is inhibited by dideoxynucleotides, and resistant to aphidicolin. The strand displacement activity of POLN was higher than exonuclease-deficient Klenow fragment. Furthermore, POLN can perform translesion synthesis past thymine glycol, a common endogenous and radiation-induced product of reactive oxygen species damage to DNA. Thymine glycol blocks DNA synthesis by most DNA polymerases, but POLN was particularly adept at efficient and accurate translesion synthesis past a 5S-thymine glycol.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • DNA Damage
  • DNA Polymerase I / biosynthesis
  • DNA Polymerase I / chemistry*
  • DNA Polymerase I / metabolism
  • DNA Replication
  • DNA-Directed DNA Polymerase / chemistry
  • Humans
  • Molecular Sequence Data
  • Protein Processing, Post-Translational
  • Recombinant Proteins / biosynthesis
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Templates, Genetic
  • Thymine / analogs & derivatives*
  • Thymine / chemistry


  • Recombinant Proteins
  • thymine glycol
  • DNA polymerase theta
  • DNA Polymerase I
  • DNA-Directed DNA Polymerase
  • Thymine