An error-correcting proofreading exonuclease-polymerase that copurifies with DNA-polymerase-alpha-primase

J Biol Chem. 1993 Mar 15;268(8):6024-33.


A DNA polymerase with a 3'-to 5'-exonuclease that copurified with polymerase-primase from calf thymus was purified and extensively characterized. Its exonuclease degraded single-stranded DNA from 3' to 5' in a strictly distributive manner. On synthetic template-primer junctions, 3'-terminal mispairs were excised with a 10- to 20-fold preference over correctly paired nucleotides. In comparison to the 3'- to 5'-exonuclease the DNA polymerase activity was rather low. The ratio of nucleotides incorporated to nucleotides excised was in the order of 1 to 3 nucleotide insertions per excision, suggesting that net forward DNA synthesis is not the primary role of this DNA polymerase. DNA synthesis was performed with a low processivity in the presence and absence of PCNA. Both the polymerase and exonuclease activities were inhibited to a comparable extent by AMP. Thus, the exonuclease-polymerase might represent a novel DNA polymerase that we tentatively designate as DNA polymerase zeta. Possible benefits of DNA polymerase zeta in the process of error correction and the apparent dichotomy of an built-in proofreading activity for the processive DNA polymerases gamma, delta, and epsilon and an obviously external proofreading function for the less processive animal cell DNA polymerases alpha and beta are discussed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Cattle
  • Chromatography, Liquid
  • DNA
  • DNA Primase
  • DNA Replication*
  • DNA-Directed DNA Polymerase / isolation & purification*
  • DNA-Directed DNA Polymerase / metabolism
  • Electrophoresis, Polyacrylamide Gel
  • Exonucleases / antagonists & inhibitors
  • Exonucleases / isolation & purification*
  • Exonucleases / metabolism
  • Molecular Sequence Data
  • Nucleic Acid Synthesis Inhibitors
  • RNA Nucleotidyltransferases / isolation & purification*
  • Substrate Specificity


  • Nucleic Acid Synthesis Inhibitors
  • DNA
  • DNA Primase
  • RNA Nucleotidyltransferases
  • DNA-Directed DNA Polymerase
  • Exonucleases