High-level expression, purification, and enzymatic characterization of full-length Thermus aquaticus DNA polymerase and a truncated form deficient in 5' to 3' exonuclease activity

PCR Methods Appl. 1993 May;2(4):275-87. doi: 10.1101/gr.2.4.275.


The Thermus aquaticus DNA polymerase I (Taq Pol I) gene was cloned into a plasmid expression vector that utilizes the strong bacteriophage lambda PL promoter. A truncated form of Taq Pol I was also constructed. The two constructs made it possible to compare the full-length 832-amino-acid Taq Pol I and a deletion derivative encoding a 544-amino-acid translation product, the Stoffel fragment. Upon heat induction, the 832-amino-acid construct produced 1-2% of total protein as Taq Pol I. The induced 544-amino-acid construct produced 3% of total protein as Stoffel fragment. Enzyme purification included cell lysis, heat treatment followed by Polymin P precipitation of nucleic acids, phenyl sepharose column chromatography, and heparin-Sepharose column chromatography. For full-length 94-kD Taq Pol I, yield was 3.26 x 10(7) units of activity from 165 grams wet weight cell paste. For the 61-kD Taq Pol I Stoffel fragment, the yield was 1.03 x 10(6) units of activity from 15.6 grams wet weight cell paste. The two enzymes have maximal activity at 75 degrees C to 80 degrees C, 2-4 mM MgCl2 and 10-55 mM KCl. The nature of the substrate determines the precise conditions for maximal enzyme activity. For both proteins, MgCl2 is the preferred cofactor compared to MnCl2, CoCl2, and NiCl2. The full-length Taq Pol I has an activity half-life of 9 min at 97.5 degrees C. The Stoffel fragment has a half-life of 21 min at 97.5 degrees C. Taq Pol I contains a polymerization-dependent 5' to 3' exonuclease activity whereas the Stoffel fragment, deleted for the 5' to 3' exonuclease domain, does not possess that activity. A comparison is made among thermostable DNA polymerases that have been characterized; specific activities of 292,000 units/mg for Taq Pol I and 369,000 units/mg for the Stoffel fragment are the highest reported.

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Cloning, Molecular
  • DNA Polymerase I / genetics*
  • DNA Polymerase I / isolation & purification
  • DNA Polymerase I / metabolism
  • DNA, Bacterial / genetics
  • Gene Expression
  • Genetic Vectors
  • Molecular Sequence Data
  • Peptide Fragments / isolation & purification
  • Peptide Fragments / metabolism
  • Polymerase Chain Reaction / methods*
  • Temperature
  • Thermus / enzymology*
  • Thermus / genetics*


  • DNA, Bacterial
  • Peptide Fragments
  • DNA Polymerase I