FIGURE 1.

The structure of the tm RB69 pol ternary complex (Protein Data Bank (PDB) accession number 3SJJ). a, ternary complex showing dUpNpp bound in the active site with metal ions A and B. b, close-up of the tm RB69 pol active site showing the B metal ion in perfect octahedral geometry and the A metal ion in a distorted octahedral geometry. c, predicted position of 3′-OH group in an idealized octahedron during the transition state. d, a close-up of the coordination complex showing the two metal ions, the 3′-OH group, and the α phosphate of the incoming dNTP.