The secondary structure (a), two views of the SAXS-derived molecular envelope (b), and the two-dimensional topological drawing (c) of riboA. In (a), A99 denotes the adenine ligand. In (b), dimensional lengths are in angstroms. In (c), the nucleotide residues are coded in same color as in (a) and the orientations and phases (Θ, Φ, ρ0) of the duplexes are obtained from the best simultaneous RDC fit, given alongside the duplexes.