Figure 3.

MagT1 is a subunit of the STT3B complex. (A, B, and D) cRM were solubilized under nondenaturing conditions and incubated with protein A–Sepharose beads with covalently coupled nonimmune (NI) IgG or anti-STT3B IgG (A and B) or noncoupled anti-STT3A IgG (D, anti-ITM1 sera). (C) HeLa cells expressing MagT1-V5 were solubilized and incubated with protein A–Sepharose beads coated with anti-V5 IgG or NI IgG. (A–D) Proteins were eluted with IP wash buffer, resolved by SDS-PAGE, and stained with silver (A) to detect major proteins including known OST subunits (STT3B, ribophorin I [Rb-1], ribophorin II [Rb-II], and OST48) or analyzed by protein immunoblotting using the indicated antisera (B–D). (B–D) Input samples (cRM [B and D] or HeLa cell extract [C]) were electrophoresed on the same gel to provide protein mobility markers. MagT1 and malectin co-migrate (B) with the 34-kD band detected by silver staining (A). Asterisks designate nonspecific bands recognized by the anti-STT3B sera on protein blots of the input samples. In B, vertical lines indicate removal of an intervening lane of molecular weight markers.