DEDDy 3'-5' exonuclease domain of Sulfolobus solfataricus DNA polymerase B1 and similar archaeal family-B DNA polymerases
The 3'-5' exonuclease domain of Sulfolobus solfataricus DNA polymerase B1 and similar archaeal proteins. B1 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. B1displays thermostable 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. Family-B DNA polymerases from thermophilic archaea are unique in that they are able to recognize the presence of uracil in the template strand, leading to the stalling of DNA synthesis. This is an additional safeguard mechanism against increased levels of deaminated bases during genome duplication at high temperatures. S. solfataricus B1 also interacts with DNA polymerase Y and may contribute to genome stability mechanisms.