Figure 3.

Structures of 3D^pol complexed with ribonucleotides in the presence of Mn²⁺ with anomalous difference maps to identify the positions of the chelated Mn²⁺ cations. (a) 2.6 Å resolution 2F_o-F_c map (green) contoured at 1.5σ around UTP and a 2.6 Å resolution anomalous map contoured at 3.5σ Mn²⁺ (blue; λ = 1.54 Å). (b) 2.5 Å resolution 2F_o-F_c map (green) contoured at 1.5σ around CTP and a 2.5 Å resolution anomalous map (blue; λ = 1.54 Å) at 3.9σ around Mn²⁺. The * marks the location of weak third peak in the anomalous difference maps. (c) 2.5 Å resolution 2F_o-F_c map (green) contoured at 1.5σ around GTP and a 2.2 Å resolution anomalous map contoured at 10.0σ around Mn²⁺ (blue; λ = 1.9 Å). (d) Comparison of divalent cation positions in poliovirus and other polymerases. The 3D^pol-GTP-Mn²⁺ structure from panel (c) is shown with its Mn²⁺ ions depicted as large stippled spheres and inside these spheres are smaller spheres corresponding to Mn²⁺ ions from panels a,b,c (blue), Mn²⁺ ions (orange) from hepatitis C virus ⁸; ¹⁰ and rabbit hemorrhagic disease virus⁵, Mg²⁺ (yellow) from bacteriophage φ6 ¹³ and Sm²⁺ (green) from human rhinovirus serotype 14 ³. The polymerase structures were superimposed using Cα atoms from the active site GDD motif and three residues on either side of it.