Park, SoyeonLi, XuemingKim, Ho MinSingh, Chingakham R.Tian, GengHoyt, Martin A.Lovell, ScottBattaile, Kevin P.Zolkiewski, MichalCoffino, PhilipRoelofs, JeroenCheng, YifanFinley, Daniel2014-01-022014-01-022014-01-02http://hdl.handle.net/2097/17009The proteasomal ATPase ring, comprising Rpt1-Rpt6, associates with the heptameric α ring of the proteasome core particle (CP) in the mature proteasome, with the Rpt C-terminal tails inserting into pockets of the α ring[superscript 1-4]. Rpt ring assembly is mediated by four chaperones, each binding a distinct Rpt subunit[superscript 5-10]. We report that the base subassembly of the proteasome, which includes the Rpt ring, forms a high affinity complex with the CP. This complex is subject to active dissociation by the chaperones Hsm3, Nas6, and Rpn14. Chaperone-mediated dissociation was abrogated by a nonhydrolyzable ATP analog, indicating that chaperone action is coupled to nucleotide hydrolysis by the Rpt ring. Unexpectedly, synthetic Rpt tail peptides bound α pockets with poor specificity, except for Rpt6, which uniquely bound the α2/α3 pocket. Although the Rpt6 tail is not visualized within an α pocket in mature proteasomes[superscript 2-4], it inserts into the α2/α3 pocket in the base-CP complex and is important for complex formation. Thus, the Rpt-CP interface is reconfigured when the lid complex joins the nascent proteasome to form the mature holoenzyme.en-USProteasomeChaperoneSingle particle cryoEMATPaseArticle (author version)