DEDDy 3'-5' exonuclease domain of Pyrococcus kodakaraensis Kod1 and similar archaeal family-B DNA polymerases
The 3'-5' exonuclease domain of archaeal family-B DNA polymerases with similarity to Pyrococcus kodakaraensis Kod1, including polymerases from Desulfurococcus (D. Tok Pol) and Thermococcus gorgonarius (Tgo Pol). Kod1, D. Tok Pol, and Tgo Pol are thermostable enzymes that exhibit both polymerase and 3'-5' exonuclease activities. They are family-B DNA polymerases. Their amino termini harbor a DEDDy-type DnaQ-like 3'-5' exonuclease domain that 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 contains a beta hairpin structure that plays an important role in active site switching in the event of nucleotide misincorporation. Members of this subfamily show similarity to eukaryotic DNA polymerases involved in DNA replication. Some archaea possess multiple family-B DNA polymerases. 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.