POLN, a nuclear PolA family DNA polymerase homologous to the DNA cross-link sensitivity protein Mus308

J Biol Chem. 2003 Aug 22;278(34):32014-9. doi: 10.1074/jbc.M305646200. Epub 2003 Jun 6.


The Drosophila Mus308 gene is unusual in encoding both a family A DNA polymerase domain and a DNA/RNA helicase domain. A mus308 mutation was shown to result in increased sensitivity to DNA cross-linking agents, leading to the hypothesis that Mus308 functions in the repair of DNA interstrand cross-links. Recently a mammalian ortholog of Mus308, POLQ, has been identified. We report here the identification, cloning, and characterization of POLN and its gene product, a new mammalian DNA polymerase also related to Mus308. The human cDNA encodes a protein of 900 amino acid residues. The region starting from residue 419 shares 33% identity (48% similarity) with the equivalent region of Escherichia coli DNA polymerase I. POLN is expressed in human cell lines with numerous alternatively spliced transcripts, and a full-length human coding region that comprises 24 exons within 160 kilobases of genomic DNA. Expression analysis by northern blotting and in situ hybridization showed highest expression of full-length POLN in human and mouse testis. POLN localized to the nucleus when expressed as a enhanced green fluorescent protein (GFP)-tagged protein in human fibroblasts. GFP-tagged recombinant POLN had DNA polymerase activity on activated calf thymus DNA and on a singly primed template.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Chromosome Mapping
  • DNA / metabolism*
  • DNA Polymerase I / chemistry
  • DNA Polymerase I / genetics
  • DNA Polymerase I / metabolism*
  • DNA Primers
  • DNA Repair Enzymes
  • DNA-Directed DNA Polymerase
  • Drosophila Proteins*
  • Humans
  • Male
  • Mice
  • Molecular Sequence Data
  • Sequence Homology, Amino Acid
  • Testis / enzymology


  • DNA Primers
  • Drosophila Proteins
  • DNA
  • DNA Polymerase I
  • DNA-Directed DNA Polymerase
  • DNApol-theta protein, Drosophila
  • DNA Repair Enzymes

Associated data

  • GENBANK/AY135562
  • GENBANK/AY136549