Schematic representation of the a) secondary and b) tertiary structure of the env8HyCbl riboswitch, complete with the Cy3 (green star), Cy5 (red star), and biotin (blue rectangle) synthetic moieties. The loops, L5 (red) and L13 (green) form a regulatory RNA kissing-loop (KL, see inset for sequence), which contains the purine-rich ribosome binding site (shadowed green nucleotides). Binding of hydroxocobalamin (bronze spheres, HyCbl) facilitates formation of the KL, which decreases the distance between the Cy3 (donor) and Cy5 (acceptor) fluorophores, and thereby resulting in increased energy transfer efficiency (EFRET).