Figure 3.

Remote structural similarity to D-(D/E)XK nucleases. (a). Schematic drawing of the structure of Ydr370C. Motif I and helix αB are shown in orange, motif II and helix αD in yellow, motif III and its associated β-strands in green, motif IV and its associated β-strands in cyan. The Mn²⁺ ion is shown as a sphere in pink. (b). Structure of herpesvirus alkaline nuclease ^19,20, in the same view as that for Ydr370C (panel a). (c). Structure of E. coli prophage RecE 5′-3′ exonuclease ²². (d). Structure of λ phage 5′-3′ exonuclease ²³. (e). Structure of type II restriction endonuclease HincII ²⁵. Residues in the four conserved motifs of Ydr370C, and their equivalents in the other enzymes, are indicated in each of the panels. A dash means that a functionally equivalent residue is absent.