Fig. 2: Structural basis for 8-oxo-rGTP discrimination opposite cytosine.

a Kinetic analysis of oxidized and undamaged (d)GTP insertion by pol μ. Catalytic efficiency is indicated as a blue line for insertion opposite template base C (C_t) and as a red line for insertion opposite template base A (A_t), in the presence of Mg²⁺ (left panel) or Mn²⁺ (right panel). Fold preference is indicated next to a blue (C_t) or red (A_t) dashed arrow. The error bars represent standard errors (S.E.) derived from three independent measurements. b Active site of the Ca²⁺-bound precatalytic ground state 8-oxo-rGTP:C_t ternary complex. Protein sidechains are shown in yellow stick representation and DNA is in cyan, Helix N is shown as a yellow cartoon. Ca²⁺ atoms are the orange spheres, waters are blue spheres. Simulated annealing (F_o–F_c) omit density (green mesh) shown is contoured at 3 σ. The σ_A (2F_o–F_c) map shown as a blue mesh is contoured at 1.5 σ with a carve radius of 1.0 Å. c Comparison of Ca²⁺-bound precatalytic ground state deoxy- (purple sidechains and DNA) and ribo-8-oxo-GTP:C_t (yellow sidechains and cyan DNA) ternary complexes. Rotation of the primer terminus (P_n) in the 8-oxo-rGTP structure is shown with a blackarrow, placing O3´ in an inverted orientation that is incompatible with attack at P_α. d Mn²⁺-ground state 8-oxo-rGTP:C_t ternary complex (15 min soak) showing 8-oxo-rGTP in an unreactive orientation. Mn²⁺ atoms are the small purple spheres, Na⁺ is shown as a larger purple sphere.