Structure-based sequence alignment of the UDG superfamily. Completely conserved residues among family 1–5 UDGs are boxed with solid lines. The location of the secondary structure elements of TthUDGV is represented at the top of sequences. The conserved motifs A and B are underlined by red lines, and the active residues are marked by red stars. Abbreviations: EcUNG, E. coli UNG; EcMUG, E. coli MUG; GmeSMUG, Geobacter metallireducens SMUG; TthUDGIV, T. thermophilus UDGIV; TthUDGV, T. thermophilus UDGV; and SacUDGV, S. acidocaldarius UDGV. The sequences of the five families’ UDGs were mutialigned using ClustalW and EXPript3.x.