Figure 8:

A single conformer of poly rU and poly rA (derived from the SAXS data), selected from the ensemble generated for each salt condition, illustrates the general trends prevalent in the models. For simplicity, we display only one structure for each condition. The full set of models required to fit the SAXS data are provided in the SI. The scrunched, ‘cage-like’ conformations of the poly rA backbones (lower structures) are present in Mg²⁺ containing solutions but absent from solutions containing only Na⁺. The former structures place backbone phosphates, sugar OH groups and base nitrogens in geometries which favor Mg²⁺ ion associations. Representative structures for each experimental condition can be found at the SASBDB codes as referenced in Figure 3.