A DNA polymerase having the following characteristics: (1) showing a polymerase activity on a complex employed as a substrate wherein a primer has been annealed with a single-stranded template DNA higher than the activity on an activated DNA employed as a substrate; (2) having a 3'}5' exonuclease activity; and (3) when subjected to a PCR reaction with the use of a lambda -DNA as a template, being capable of amplifying a DNA fragment of about 20 kbp without the necessity for adding any other enzyme; a protein constituting the DNA polymerase; a DNA containing a base sequence encoding the same; and a process for producing the DNA polymerase. This DNA polymerase is a novel one having both of a high primer extensibility and the 3'}5' exonuclease activity.
