In addition to polymerase activity, this DNA polymerase exhibits 3' to 5' exonuclease activity. PI-ThyI and PI-ThyII are endonucleases. PI-ThyI cleaves the inteinless sequence of the Thy DNA pol gene. It requires a 21-bp minimal recognition sequence. a 2'-deoxyribonucleoside 5'-triphosphate + DNA(n) = diphosphate + DNA(n+1) This protein undergoes a protein self splicing that involves a post-translational excision of the intervening region (intein) followed by peptide ligation. Belongs to the DNA polymerase type-B family.