This domain belongs to human mitochondrial DNA polymerase (Pol-gamma). Pol-gamma has a catalytic subunit, Pol gamma-A, which possesses both polymerase and proofreading exonuclease activities and an accessory subunit, Pol gamma-B, which accelerates polymerization rate and suppresses exonuclease activity. This domain is the exonuclease domain of the catalytic subunit, Pol gamma-A [1].

1: Structural insight into processive human mitochondrial DNA synthesis and disease-related polymerase mutations. Lee YS, Kennedy WD, Yin YW; Cell. 2009;139:312-324. PMID:19837034