Preliminary X-ray crystallographic and NMR studies on the exonuclease domain of the ε subunit of Escherichia coli DNA polymerase III

The structured core of the N-terminal 3'-5' exonuclease domain of ε, the proofreading subunit of Escherichia coli DNA polymerase III, was defined by multidimensional NMR experiments with uniformly ¹⁵N-labeled protein: it comprises residues between IIe-4 and Gln-181. A 185-residue fragment, termed ε(1-185), was crystallized by the hanging drop vapor diffusion method in the presence of thymidine-5'-monophosphate, a product inhibitor, and Mn²⁺ at pH 5.8. The crystals are tetragonal, with typical dimensions 0.2 mm x 0.2 mm x 1.0 mm, grow over about 2 weeks at 4°C, and diffract X-rays to 2.0 Å. The space group was determined to be P4(n)2₁2 (n = 0, 1, 2, 3), with unit cell dimensions a = 60.8 Å, c = 111.4 Å. (C) 2000 Academic Press.