Trapping of BACE476Δ by OS-9.1 upon inactivation of the HRD1 pathway. (A) BACE476Δ was immunoisolated from detergent extracts of cells incubated with a scrambled siRNA, and siRNA targeting HRD1, GP78, GP78, and HRD1 (lanes 1–4) and SEL1L, OS-9, XTP3-B, and XTP3-B + OS-9 (lanes 6–9, respectively). Proteins were separated in SDS polyacrylamide gels and transferred on PVDF. The membranes were blotted with antibodies recognizing endogenous GRP94, BiP, OS-9.1, and OS-9.2 and BACE476Δ as a loading control. (B) Same as described in A for BACE476. Arrowheads indicate the coprecipitated OS-9.1. TCE, total cell extract; IP, immunoprecipitation.