DEDDy 3'-5' exonuclease domain of eukaryotic DNA polymerase epsilon, a family-B DNA polymerase
The 3'-5' exonuclease domain of eukaryotic DNA polymerase epsilon. DNA polymerase epsilon is a family-B DNA polymerase with a catalytic subunit that contains a DEDDy-type DnaQ-like 3'-5' exonuclease domain. It is one of the three DNA-dependent type B DNA polymerases (alpha and delta are the other two) that have been identified as essential for nuclear DNA replication in eukaryotes. DNA polymerase epsilon plays a role in elongating the leading strand during DNA replication. It is also involved in DNA repair. The catalytic subunit contains both polymerase and 3'-5' exonuclease activities. The N-terminal exonuclease domain contains three 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 are involved in metal binding and catalysis. DNA polymerase epsilon also carries a unique large C-terminal domain with an unknown function. Phylogenetic analyses indicate that it is orthologous to the archaeal DNA polymerase B3 rather than to the eukaryotic alpha, delta, or zeta polymerases. The exonuclease domain of family-B polymerases contains a beta hairpin structure that plays an important role in active site switching in the event of nucleotide misincorporation
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