To detect proteins by immunoblotting, samples run in denaturing or nondenaturing gels were transferred to PVDF membranes (Millipore). The following primary antibodies were used in this study: anti-α4/Pre6 (D. Wolf), anti-Rpt1 (Enzo Life Sciences), anti-Rpt2 (Enzo Life Sciences), anti-Rpt3 (Enzo Life Sciences), anti-Rpt4 (W. Tansey), anti-Rpt5 (Enzo Life Sciences), anti-Rpt6 (C. Mann), anti-Rpn12 (D. Finley), anti-Hsm3, anti-Nas2, and anti-Nas6 (all Hochstrasser lab stocks; Funakoshi et al., 2009 (link)); anti-FLAG (Sigma-Aldrich), anti-GFP/JL8 (TaKaRa), and Pgk1 (Invitrogen). Secondary antibodies used for enhanced chemiluminescence were anti-mouse IgG, horseradish peroxidase (HRP)-linked (from sheep) and anti-Rabbit IgG, HRP-linked (from donkey) (both GE Healthcare).