Pull-down analysis of HupF interactions with HupL and HupK proteins. Proteins were resolved by SDS-PAGE (top panels) or 4-20% gradient native PAGE (bottom panels). Immunoblots were revealed with antisera raised against HupL (panel A) or HupK (panel C), or with StrepTactin-alkaline phosphatase conjugate (panel B) to detect HupFST. Eluates (E) were obtained from extracts from R. leguminosarum UPM 1155 derivative strains harboring pALPF1-derivative plasmids deficient in hupD (pALPF4) or in hupK (pALPF10) and expressing HupFST from plasmid pPM501. Soluble extracts (S) of the corresponding cultures were loaded as controls for detection of HupL and HupK proteins. Arrows indicate the relevant bands identified in the eluate from the ΔhupD mutant. Proteins subjected to SDS-PAGE (top panels) were loaded in gels with different amounts of polyacrylamide (9% for HupL, 15% for HupFST, and 12% for HupK). Numbers on the left margin of the panels indicate the position of molecular weight standards (kDa, top panels), or the position of BioRad Precision Plus Standards (1, 250 kDa; 2, 150 kDa, 3, 75 kDa; 4, 100 kDa) in native gels (bottom panels).