Deletion of TRAPβ/SSR2 or TRAPδ/SSR4 in INS832/13 cells. A, TRAPβ/SSR2 or TRAPδ/SSR4 null cells and corresponding control cells (CON) were immunoblotted with the antibodies indicated. Tubulin is a loading control. B, Quantitation of TRAP/SSR subunits from experiments like that in panel A (n = 4). C, Quantitation of proinsulin and insulin from experiments like that in panel A (n = 4). *P < .05, **P < .01 compared to Control. D, TRAPβ/SSR2 or TRAPδ/SSR4 null cells were pulse-labeled with 35S-Met/Cys for 30 minutes (left panel) before immunoprecipitation with anti-insulin, followed by SDS-PAGE and phosphorimaging. Quantitation of newly-synthesized proinsulin (PI, mean ± SD) is shown *P < .05 compared to Control (n = 4)