TAP-MS was performed as previously described (Pu et al., 2015 (link)). In brief, HeLa or H4 cells stably expressing proteins tagged with N-terminal OSF or C-terminal FOS were extracted with 1% Triton X-100, 50 mM Tris-HCl, pH 7.4, 300 mM NaCl, and 5 mM EDTA, supplemented with proteinase inhibitor cocktail (Roche). After clearing by centrifugation for 15 min at 17,000 g, proteins were sequentially purified on Strep-Tactin (IBA) and FLAG antibody–coated beads (Sigma-Aldrich). Beads were washed with 0.2% Triton X-100, 50 mM Tris-HCl, pH 7.4, 300 mM NaCl, and 5 mM EDTA, and bound proteins were eluted with 2.5 mM desthiobiotin and 150 ng/ml of 3× FLAG peptide (Sigma-Aldrich), respectively. Proteins were precipitated with 10% TCA, washed with acetone, air-dried, and analyzed by liquid chromatography (LC)/MS at the Taplin MS facility (Harvard Medical School, Boston, MA). The results of MS analysis for OSF-BLOS2 are shown in Table S1 from Pu et al. (2015) (link), and those for OSF-lyspersin, lyspersin-FOS, and OSF-Pallidin are shown in in Tables S1, S2, and S3 of the current study.