Fig. 1.

Secondary structure of preQ₁-II riboswitches. (A) Predicted secondary structure of the Spn riboswitch. Labeling of stems and loops is based on standard H-type pseudoknot nomenclature (73). Numbering of helices (P) and labeling of junction nucleotides (J) is based on ref. 39. (B) Determined secondary structure of Spn. (C) Determined secondary structure of Lra (39). Hydrogen bond interactions are shown using the Leontis and Westhof notation (74). The color scheme for structural elements used in this figure is consistent throughout the other figures unless noted otherwise.