Proteasomal ubiquitin receptor ADRM1 is a protein that in humans is encoded by the ADRM1 gene. Recent evidences on proteasome complex structure confirmed that the protein encoded by gene ADRM1, also known in yeast as 26S Proteasome regulatory subunit Rpn13 (systematic nomenclature for proteasome subunits), is a subunit of 19S proteasome complex. Gene The gene ADRM1 encodes one of the non-ATPase subunits of the 19S regulator base, subunit Rpn13. The human PSMD4 gene has 10 exons and locates at chromosome band 20q13.33.The human protein Proteasomal ubiquitin receptor ADRM1 is 42 kDa in size and composed of 407 amino acids. The calculated theoretical pI of this protein is 4.95. Structure The protein encoded by this gene is an integral plasma membrane protein which promotes cell adhesion. The encoded protein is thought to undergo O-linked glycosylation. Expression of this gene has been shown to be induced by gamma interferon in some cancer cells. Two transcript variants encoding the same protein have been found for this gene. Complex assembly 26S proteasome complex is usually consisted of a 20S core particle (CP, or 20S proteasome) and one or two 19S regulatory particles (RP, or 19S proteasome) on either one side or both side of the barrel-shaped 20S. The CP and RPs pertain distinct structural characteristics and biological functions. In brief, 20S sub complex presents three types proteolytic activities, including caspase-like, trypsin-like, and chymotrypsin-like activities. These proteolytic active sites located in the inner side of a chamber formed by 4 stacked rings of 20S subunits, preventing random protein-enzyme encounter and uncontrolled protein degradation. The 19S regulatory particles can recognize ubiquitin-labeled protein as degradation substrate, unfold the protein to linear, open the gate of 20S core particle, and guide the substate into the proteolytic chamber. To meet such functional complexity, 19S regulatory particle contains at least 18 constitutive subunits. These subunits can be categorized into two classes based on the ATP dependence of subunits, ATP-dependent subunits and ATP-independent subunits. According to the protein interaction and topological characteristics of this multisubunit complex, the 19S regulatory particle is composed of a base and a lid subcomplex. The base consists of a ring of six AAA ATPases (Subunit Rpt1-6, systematic nomenclature) and four non-ATPase subunits (Rpn1, Rpn2, and Rpn10. Thus, Proteasomal ubiquitin receptor ADRM1 (Rpn13) is an important component of forming the base subcomplex of 19S regulatory particle. Traditional view of Rpn13 is that it is rather an associating