Abstract: Recombinant DNA sequences encoding the DNA polymerase activity of Pyrodictium species can be used to construct recombinant vectors and transformed host cells for production of the activity. Pyrodictium enzymes for catalyzing 3'.fwdarw.5' exonuclease activity, i.e., proofreading enzymes, are also provided. The Pyrodictium enzymes are useful in DNA amplification procedures and are not irreversibly inactivated by exposure to 100.degree. C. in a polymerase chain reaction.