Fig. 3: Crystal structure of NtMOC1 in complex with a synthetic HJ.

a Two perpendicular views of the complex structure. Subunits of the protein dimer are shown in slate and yellow. The four DNA strands C, D, E, and F are colored in pink, wheat, cyan, and green, respectively. The HJ is embedded into the cleft of the dimeric enzyme. b Structure of the HJ in the complex. The electron density map is contoured at 1.0 σ. Scissors indicate the scissile phosphates. Distances between the exchanging and non-exchanging strands are measured. c Active centers of NtMOC1. The magnesium ions are shown as purple spheres. Four acidic amino acids, coordinating with magnesium, constitute the catalytic tetrad. d Mutations at the catalytic tetrad of NtMOC1 have no effect on the HJ binding activity. e Mutations at the catalytic tetrad of NtMOC1 abolish the HJ cleavage activity. For the HJ binding and cleavage assay, X2 (CCGG) was used as HJ substrate. The final concentration of HJ in each lane was 250 nM. Five gradients with increasing concentrations (0, 125, 250, 500, and 1000 nM) were applied for each protein sample. The reactions were resolved by native PAGE and visualized by GelRed staining. Source data are provided as a Source Data file.