DEDDy 3'-5' exonuclease domain of Escherichia coli DNA polymerase II and similar bacterial family-B DNA polymerases
The 3'-5' exonuclease domain of Escherichia coli DNA polymerase II (Pol II) and similar bacterial proteins. Pol II 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. 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 has a fundamental role in the proofreading activity of polII. It contains a beta hairpin structure that plays an important role in active site switching in the event of a nucleotide misincorporation. Pol II is involved in a variety of cellular activities, such as the repair of DNA damaged by UV irradiation or oxidation. It plays a pivotal role in replication-restart, a process that bypasses DNA damage in an error-free manner. Pol II is also involved in lagging strand synthesis.