Figure 1.

Schematic diagrams showing the various tetraloop motifs and their hydrogen-bonding interactions, adapted from Hsiao et al. (11), Figure 3. (a) The standard tetraloop. (b) A tetraloop with a 3–2 switch where the bases of the j+2 and the j+3 residues are switched. (c) A tetraloop with insertion where a residue (in pink) is inserted between the j+1 and the j+2 residues. However, >1 residue can be inserted and if extensive enough, would produce a strand clip. (d) A tetraloop with deletion where the j+2 residue in the standard tetraloop is absent so the j+3 residue becomes the j+2 residue. Rectangles, pentagons and circles denote base, sugar and phosphate groups, respectively, while dashed lines denote characteristic hydrogen bonds.