Structure of the KsgA-RNA-SAH complex (Tu, Tropea, Austin, Court, Waugh and Ji. Structure 2009; 16:1417-1427. Abstract). (A) Front view of the complex: protein as a ribbon diagram in white; substrate RNA as a tube-and-stick model in light orange with the adjacent A1518 and A1519 highlighted in magenta; and cofactor SAH as a stick model in green. Roman numerals indicate the conserved structural motifs of the protein: well conserved motifs I-IV, VIII and X in blue; less conserved motifs V-VII in cyan. (B) Six strong hydrogen bonds (dashed lines) are observed between the protein and the RNA in the complex. Amino acid residues interacting with the bound RNA are shown as thicker sticks while the nucleotide residues are shown as thinner sticks. Hydrogen bonds 1, 2 and 5 (colored in red) involve the O2' hydroxyl groups of nucleotide resides.