This domain has 3' to 5' exonuclease activity and adopts a ribonuclease H type fold.

1: Crystal structures of an NH2-terminal fragment of T4 DNA polymerase and its complexes with single-stranded DNA and with divalent metal ions. Wang J, Yu P, Lin TC, Konigsberg WH, Steitz TA; Biochemistry 1996;35:8110-8119. PMID:8679562

2: Crystallization and preliminary diffraction analysis of a hyperthermostable DNA polymerase from a Thermococcus archaeon. Zhou M, Mao C, Rodriguez AC, Kiefer JR, Kucera RB, Beese LS; Acta Crystallogr D Biol Crystallogr 1998;54:994-995. PMID:9757117