FIGURE 3.

Metal ion-binding site. A, intact ttRecJ ligand-free form. B, Mn²⁺ ion-binding sites in intact ttRecJ. Electron density (magenta) of the Mn²⁺ ions derived from an anomalous difference Fourier map (λ = 1.70000 Å) is superimposed on the model. The position of the Mn²⁺ ion is shown by a magenta sphere. Water molecules are shown by cyan spheres. C, Mg²⁺ ion-binding site in intact ttRecJ. The position of the Mg²⁺ ion is shown by a red sphere. D, Mn²⁺ ion-binding site in cd-ttRecJ (Protein Data Bank code 1IR6). The position of the Mn²⁺ ion is shown by a magenta sphere. Wat¹ (W1) is assumed to be the nucleophilic water. The motif names are indicated in parentheses. The dashed lines show the coordination with the metal ion.