inactive DEDDy 3'-5' exonuclease domain of Bacillus stearothermophilus DNA polymerase I and similar family-A DNA polymerases
Bacillus stearothermophilus-like Polymerase I (Pol I), a subgroup of the family-A DNA polymerases, contains an inactive DnaQ-like 3'-5' exonuclease domain in the same polypeptide chain as the polymerase region. The exonuclease-like domain of these proteins possess the same fold as the Klenow fragment (KF) of Escherichia coli Pol I, but does not contain the four critical metal-binding residues necessary for activity. The function of this domain is unknown. It might act as a spacer between the polymerase and the 5'-3' exonuclease domains. Some members of this subgroup, such as those from Bacillus sphaericus and Thermus aquaticus, are thermostable DNA polymerases.