DEDDy 3'-5' exonuclease domain of Escherichia coli DNA polymerase I and similar bacterial family-A DNA polymerases
Escherichia coli-like Polymerase I (Pol I), a subgroup of family-A DNA polymerases, contains a DEDDy-type DnaQ-like 3'-5' exonuclease domain in the same polypeptide chain as the polymerase domain. The exonuclease domain contains three conserved sequence motifs termed ExoI, ExoII and ExoIII, with a specific YX(3)D pattern at ExoIII. These motifs are clustered around the active site and contain four conserved acidic residues that serve as ligands for the two metal ions required for catalysis. The 3'-5' exonuclease domain of DNA polymerases has a fundamental role in reducing polymerase errors and is involved in proofreading activity. E. coli DNA Pol I is involved in genome replication but is not the main replicating enzyme. It is also implicated in DNA repair.