Thermo Scientific DNA Polymerase I possesses 5′?3′ DNA synthesis activity, 3′?5′ exonuclease (proofreading) activity, and 5′?3′ exonuclease activity. Klenow Fragment is the large fragment of DNA polymerase I. It exhibits 5′?3′ polymerase activity and 3′?5′ exonuclease (proofreading) activity, but lacks 5′?3′ exonuclease activity. Klenow Fragment, exo-, is also the large fragment of DNA polymerase I. It exhibits 5′?3′ polymerase activity, but lacks the 3′?5′ and 5′?3′ exonuclease activities.