Multi-angle light scattering (MALS) studies were performed inline with size-exclusion chromatography on protein and RNA samples to assess monodispersity and mass of the SAXS samples using an 18-angle DAWN HELEOS light scattering (LS) detector in which detector 12 was replaced with a DynaPro quasi-elastic light scattering detector (Wyatt Technology). Simultaneous concentration measurements were made with an Optilab rEX refractive index detector (Wyatt Technology) connected in tandem to the LS detector. For each buffer used, the MALS system was calibrated with BSA at 10 mg/mL to determine delay times and band broadening. For proteins, BSA, xylanase and glucose isomerase provided an additional calibration of the refractive index increment for protein samples. For RNA samples, the refractive index increment was determined from P4–P6 RNA samples10 (link), 30 (link).
MALS analyses were performed on all the RNAs (except tRNAphe) in this study and a set of proteins comprising glucose isomerase, xylanase, thermosome, catalase, TBL1, PYR1, and p65 (Table S1 and S2).