This is the C-terminal domain found in RPN1 proteins (26S proteasome non-ATPase regulatory subunit 2). The 26S proteasome holocomplex consists of a 28-subunit barrel-shaped core particle (CP) in the center capped at the top and bottom by 19-subunit regulatory particles (RPs). The CP forms the catalytic chamber and the RP is formed from two subcomplexes known as the lid and the base [1]. The lid comprises nine Rpn subunits in yeast (Rpn3/5/6/7/8/9/11/12/15) and the base comprises three Rpn subunits (Rpn1/2/13) and six ATPases (Rpt1-6) [2].

1: Structural basis for dynamic regulation of the human 26S proteasome. Chen S, Wu J, Lu Y, Ma YB, Lee BH, Yu Z, Ouyang Q, Finley DJ, Kirschner MW, Mao Y; Proc Natl Acad Sci U S A. 2016;113:12991-12996. PMID:27791164

2: Structure of an endogenous yeast 26S proteasome reveals two major conformational states. Luan B, Huang X, Wu J, Mei Z, Wang Y, Xue X, Yan C, Wang J, Finley DJ, Shi Y, Wang F; Proc Natl Acad Sci U S A. 2016;113:2642-2647. PMID:26929360

3: Deep classification of a large cryo-EM dataset defines the conformational landscape of the 26S proteasome. Unverdorben P, Beck F, Sledz P, Schweitzer A, Pfeifer G, Plitzko JM, Baumeister W, Forster F; Proc Natl Acad Sci U S A. 2014;111:5544-5549. PMID:24706844