Homology model of the SfiI monomer. A) Superposition of the BglI template structure (red) and the SfiI model (blue). The CCGG half-site of the DNA target is shown in green. The Ca2+ ions from the BglI structure are shown as white dots. B) SfiI model colored according to the sequence conservation: residues identical between SfiI and BglI are shown in blue, residues with physico-chemically similar side chains are in green, dissimilar residues are in yellow and red. The putative conserved active site is shown in the wireframe representation.