Fig. 2

Time-lapse crystallography and the structure of the ground state pre-catalytic ternary complex of pol μ. a Soaking binary complex (BC, black) crystals (gapped DNA/protein) of pol μ in a cryo-solution containing CaCl₂ and the incoming nucleotide (TTP) for 15 min results in formation of the Ca²⁺-bound pre-catalytic GS (yellow) ternary complex. Subsequent soaking of the GS in a cryo-solution at 4 °C containing 10 mM MgCl₂ (green) or 10 mM MnCl₂ (purple) initiates the reaction in the crystal. Crystals are frozen after increasing incubation times (green and purple arrows) and the structure of the complex is determined. b The active site of the Ca²⁺-bound pre-catalytic GS ternary complex. The incoming nucleotide (green stick), Ca²⁺ ions (yellow spheres), primer terminus and templating adenine base (cyan stick), as well as key active site residues (yellow stick) are shown. The F_o–F_c simulated annealing omit map (green mesh) shown is countered at 2.5σ. c A 90° rotation of the active site in comparison to b with metal-coordinating ligands indicated by dashes. Metal coordination is illustrated with dashed lines with distances (Å) indicated. The distance between O3′ and Pα is shown as a red dashed line