an uncharacterized bacterial subgroup of the DEDDh 3'-5' exonuclease domain family with similarity to the epsilon subunit of DNA polymerase III
This subfamily is composed of uncharacterized bacterial proteins with similarity to the epsilon subunit of DNA polymerase III (Pol III), a multisubunit polymerase which is the main DNA replicating enzyme in bacteria, functioning as the chromosomal replicase. The Pol III holoenzyme is a complex of ten different subunits, three of which (alpha, epsilon, and theta) compose the catalytic core. The Pol III epsilon subunit, encoded by the dnaQ gene, is a DEDDh-type 3'-5' exonuclease which is responsible for the proofreading activity of the polymerase, increasing the fidelity of DNA synthesis. It contains three conserved sequence motifs termed ExoI, ExoII and ExoIII, with a specific Hx(4)D conserved 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 epsilon subunit of Pol III also functions as a stabilizer of the holoenzyme complex.