DEDDy 3'-5' exonuclease domain of Sulfurisphaera ohwakuensis DNA polymerase B3 and similar archaeal family-B DNA polymerases
The 3'-5' exonuclease domain of archaeal proteins with similarity to Sulfurisphaera ohwakuensis DNA polymerase B3. B3 is a family-B DNA polymerase. Family-B DNA polymerases contain an N-terminal DEDDy DnaQ-like exonuclease domain in the same polypeptide chain as the polymerase domain, similar to family-A DNA polymerases. B3 exhibits both polymerase and 3'-5' exonuclease activities. This 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. The exonuclease domain of family B polymerases also contains a beta hairpin structure that plays an important role in active site switching in the event of nucleotide misincorporation. Archaeal proteins that are involved in DNA replication are similar to those from eukaryotes. Some archaea possess multiple family-B DNA polymerases. B3 is mainly found in crenarchaea. Phylogenetic analyses of eubacterial, archaeal, and eukaryotic family B-DNA polymerases support independent gene duplications during the evolution of archaeal and eukaryotic family-B DNA polymerases.