Source 15q column

All proteins were expressed in E. coli Rosetta cells (Sigma-Aldrich). Protein expression was induced by 0.5 mM IPTG at 20°C overnight. Cells were lysed in a lysis buffer containing 50 mM Tris, pH 8.0, 300 mM NaCl, 0.5 mM TCEP, 1 mM PMSF, and 5 mg/L aprotinin. The GST-tagged proteins were pulled down using Glutathione Sepharose 4B resin and the His-tagged DDX39B was pulled down using Ni Sepharose resin (Cytiva). GST-tagged DDX39B-CTD variants were digested with GST-TEV overnight and purified on a Source 15Q column (Cytiva). The proteins were then passed over Glutathione Sepharose 4B resin to remove remaining GST and uncleaved protein. Purified DDX39B-CTD variants were concentrated, aliquoted, and stored at −80°C in 10 mM Tris, pH 8.0, 300 mM NaCl, 0.5 mM TCEP, and 10% glycerol. The other affinity-purified proteins were first purified on a mono Q column and were subjected to overnight digestion with GST-TEV (for GST-tagged proteins) or His-TEV (for His-tagged DDX39B) to remove the affinity tag. The digested proteins were passed over Glutathione Sepharose 4B resin or Ni Sepharose resin to remove uncleaved protein and TEV. The proteins were further purified on a Superdex 200 column equilibrated with 10 mM Tris, pH 8.0, 150 mM NaCl, and 0.5 mM TCEP. All purified proteins were concentrated, aliquoted, flash frozen in liquid nitrogen, and stored at −80°C.