Proofreading by the epsilon subunit of Escherichia coli DNA polymerase III increases the fidelity of calf thymus DNA polymerase alpha

Proc Natl Acad Sci U S A. 1989 May;86(9):3085-8. doi: 10.1073/pnas.86.9.3085.


Addition of the 3'----5' proofreading exonuclease, epsilon subunit of Escherichia coli DNA polymerase III, to DNA polymerase alpha from calf thymus has been studied. Alone, calf thymus DNA polymerase alpha terminates in vitro DNA synthesis upon insertion of noncomplementary nucleotides. Upon addition of the epsilon subunit, DNA polymerase alpha elongates the newly synthesized DNA as a result of hydrolysis of the 3'-terminal mispair. The fidelity of DNA polymerase alpha in vitro is increased 7-fold by addition of the exonuclease. The functional interaction between DNA polymerase alpha and the epsilon subunit is independent of any detectable physical association. This suggests that a mechanism for proofreading could exist in mammalian cells involving sequential catalysis by DNA polymerase alpha excision of errors by a separate 3'----5' exonuclease, and further elongation onto correctly base-paired 3' termini by DNA polymerase alpha.

Publication types

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

MeSH terms

  • Animals
  • Bacteriophage phi X 174 / genetics
  • Cattle
  • DNA / biosynthesis
  • DNA Polymerase II / metabolism*
  • DNA Polymerase III / metabolism*
  • DNA, Viral / metabolism
  • DNA-Directed DNA Polymerase / metabolism*
  • Deoxyribonucleotides / metabolism
  • Escherichia coli / enzymology*
  • Exodeoxyribonuclease V
  • Exodeoxyribonucleases / metabolism
  • Kinetics
  • Nucleic Acid Hybridization
  • Thymine Nucleotides / metabolism
  • Thymus Gland / enzymology*


  • DNA, Viral
  • Deoxyribonucleotides
  • Thymine Nucleotides
  • DNA
  • DNA Polymerase II
  • DNA Polymerase III
  • DNA-Directed DNA Polymerase
  • Exodeoxyribonucleases
  • Exodeoxyribonuclease V
  • thymidine 5'-triphosphate