Fig. 3.

Structure of the RNA aptamer. (a) Overall structure of the α-p50 RNA aptamer. Residues 1–15 representing one strand are cyan, and residues 16–29 representing the other strand are orange. (b) A close-up view of the folded structure of the internal loop. Three cross-strand-stacked guanines are indicated. The non-Watson–Crick hydrogen bond pairing between U⁶ and C²⁴ and between A⁹ and G²² of the internal loop are indicated. (c) Surface presentation (23) of the RNA in two orientations related by 180° rotation around the long axis. The image on the left is in the same orientation as a and shows the narrow minor-groove section near the internal loop. The image on the right shows the protein-binding groove of the RNA.