Fig. 1: Structure of BsmI.

A Tertiary structure of the enzyme in complex with its cognate DNA. The N-terminal contains the first mixed β-sheet flanked by α-helices and carrying the bottom-strand nicking catalytic residues. The primary and tertiary structure presents similarities with the EcoRI catalytic domain. The C-terminal contains the other mixed β-sheet flanked by α-helices and carrying the top-strand nicking catalytic residues. The primary and tertiary structure presents similarities with the FokI catalytic domain. The central domain contains a smaller mixed β-sheet surrounded by smaller α-helices. The tertiary structure presents no detectable global similarity with known structures in the PDB. B Delimitation of the three domains. The green domain corresponds to the EcoRI-like domain, also called bottom-strand nicking domain, the blue domain corresponds to the central domain and the orange domain corresponds to the FokI-like domain also called top-strand nicking domain. The dark grey chain represents the DNA bottom strand, the light grey chain the DNA top strand. C Secondary structures of the enzyme. The residue numbers delimit the β-strands and the α-helices. The catalytic motifs residues are indicated with white rounded rectangles. The grey band on the fourth β-strand of the top-strand nicking domain signals the position of the retractable “insulator loop”.