Fig. 3. (A) Stereo view of the lowest energy structure of the AGAA tetraloop. The view is into the minor groove side of the loop. Two potential hydrogen bonds in the tetraloop are indicated with dashed lines, G7H22–G7 O2P and A9 H62–A6 N3. The arrow points to the ‘turning’ phosphate. (B) Top view of the sheared A–A base pair stacked on the closing C·G base pair. (C) Top view showing the stacking interactions of the four bases of the AGAA tetraloop.