DNA Polymerase  (pol ) was modeled based on the 4ZTZ crystal structure . Only the catalytic subunit, pol A, was modelled and used for further calculations. The missing regions were modeled using Rosetta Fold . Multiple structures were created, and the best structure based on preliminary visual inspection, followed by determination of the RMSD after overlay with the crystal structure, was selected as described in our previous work . The two ions in the active site were then introduced, and two different ternary systems were generated, one with Mg 2+ ions in the active site, and the other with Mn 2+ ions.