Part A. Scheme for a grid search in polar coordinatesystem (φ,θ,r) and the four possible orientations (O1 - O4) of monomeric sub-unit in the tetraloop-receptor RNA:RNA complex. Part B. Structures of the tetraloop-receptor RNA:RNA homodimer: green, determined with NMR data alone including 72 inter-subunit NOE restraints; red, determined by grid search without inter-subunit NOEs; cyan, refined with both SAXS and NMR data. The interfaces of the homodimer are indicated by the black arrows.