Structure of the Mango I aptamer. (A) Crystal structure of the aptamer bound to TO1-b (orange). The quadruplex is colored by residue, with G green, A yellow, C blue, and U red. The stem nucleotides are gray. Edges (i, ii, iii, and iv) are highlighted with a gray background. Structurally required potassium ion is shown as a purple sphere. (B) Abstract representation of the Mango I structure from the same perspective. Guanosine residues and A/U flaps are represented as rectangles. The edge that each guanosine belongs to is indicated by the Roman numeral inside the rectangle. Numbers represent nucleotide position 5′–3′. Covalent connectivity between residues is indicated by arrows. For guanosine residues, darker shading represents a lower position in the quadruplex tier. TO-1 biotin is shown as yellow.
