The proteasome is a protease complex composed of a core particle (CP) and regulatory particles (RPs) that bind to both ends of the CP. ECM29 is a protein that associates with the proteasome and is involved in the maintenance and regulation of the proteasome assembly. However, ECM29 deficient mice can form functional proteasome. In this paper we sought to identify the mechanisms and/or proteins that help and allow the maintenance of the proteasome activity in the absence of ECM29. We analyzed the proteasome components of ECM29-deficient mice and identified Hsp90 as a protein associated with the proteasome. Furthermore, the inhibition of Hsp90 led to a partial disassembly of the proteasome only in ECM29-deficient cells. Those findings attest to the importance of Hsp90 for the maintenance of the proteasome integrity in the absence of ECM29.