Usp14LF associates with proteasomes and restores the levels of ubiquitin in axJ mice. A, The left panel shows the immunoblot of proteasome fractions from the brains of wild-type (wt), axJ, and axJ Tg mice probed with polyclonal Usp14 antisera. The blots also were probed for the 19S proteasomal component Rpt4 as a positive control for proteasomes. The right panel shows catalytically active DUBs from neuronal proteasome fractions from wt, axJ, and axJ Tg mice that were labeled with HA-Ub-VME and immunoblotted with the anti-HA mAb 12CA5. The identities of the known DUBs are indicated at the right. B, Immunoblot analysis of hippocampal proteasome fractions from wild-type mice and wild-type mice containing the Usp14LF transgene (wt Tg) probed for Usp14 and the control 19S proteasomal component Rpt1 (left panel) and active DUBs labeled with HA-Ub-VME and immunoblotted with the anti-HA mAb 12CA5 (right panel). Graphs depict quantitation of the blots. C, Immunoblot analysis of hippocampal extracts measuring levels of conjugated and monomeric ubiquitin in wild-type, axJ, and axJ Tg mice. As loading controls the blots were reprobed with a monoclonal antibody to β-actin. Error bars indicate SE.