Synchrotron SAXS data from solutions of the SAM riboswitch element A aptamer domain in 50 mM potassium phosphate, 135 mM NaCl, 5 mM MgCl2, pH 6.5 were collected on the BioCAT 18ID beam line at the Advanced Photon Source (APS), Argonne National Laboratory (Lemont, IL, USA) using a Eiger2 XE 9M (Dectris) detector at a sample-detector distance of 3.7 m and at a wavelength of λ = 0.1033 nm (I(s) vs s, where s = 4πsinθ/λ, and 2θ is the scattering angle). In-line co-flow size-exclusion chromatography (SEC) SAS was employed. The SEC parameters were as follows: A 200.00 μl sample at 2.5 mg/ml was injected at a 0.60 ml/min flow rate onto a GE Superdex 200 Increase 10/300 column at 22°C. 2771 successive 0.500 second frames were collected through the entire SEC elution. The data were normalized to the intensity of the transmitted beam and radially averaged; the scattering of the solvent-blank was subtracted.
The SAM riboswitch element A sequence from Listeria monocytogenes was truncated to the conserved aptamer domain. Two non-native G residues were added to the 5' end of the molecule to facilitate in vitro transcription of the RNA with T7 RNA polymerase. Two non-native C residues were included at the 3' end of the molecule to form two stabilizing G-C base pairs at the bottom of the P1 stem.
s, nm-1
