Sequence alignment and structure of H-N-H nucleases. (A) Multiple alignment of human EndoG H-N-N motif with H-N-H nucleases. Amino acid sequences of human EndoG, NucA, Serratia nuclease, ColE9, I-Ppo I, and T4 endoVII were aligned. The amino acid residues representing the H-N-H motif are highlighted in red. The two β-strands and the α-helix of H-N-H motif are indicated by arrows and tube, respectively. The amino acid residues acting as general bases are highlighted in grey. Boxed residues represent the amino acid residues involved in magnesium coordination. (B) Comparison of the modeled structure of human EndoG and the experimentally solved structure of NucA (PDB code 1ZM8). ββα-Me-finger motif is highlighted in purple. Amino acid residues involved in catalysis, magnesium coordination, and substrate specificity are indicated and labeled.