InterPro domain: IPR032157

The 26S proteasome plays a critical role in a number of cellular processes including cell-cycle control, transcription, signal transduction and DNA repair [ 1 ]. This complex is composed of a catalytic 20S proteasome and two axially positioned 19S regulatory complexes. The overall structure is highly conserved among eukaryotes and is essential for cell viability. Assembly of the catalytic 20S proteasome CP (core particle) initiates with the formation of rings composed of seven alpha subunits and involves proteasome-assembly chaperones PAC1-PAC2, PAC3-PAC4 and UMP1 [ 2 ]. Two heterodimeric proteasome-assembly chaperones, PAC1-PAC2 and PAC3-PAC4, interact with alpha subunits and promote the correct assembly of alpha rings. PAC3-PAC4 leaves the complex during subsequent assembly of beta subunits, while PAC1-PAC2 remains bound until the assembly of the CP is completed [ 3 ].

This family consists of proteasome assembly chaperone 4 (PAC4, PSMG4). At the very C terminus there is a crucial HbYX or hydrophobic-tyrosine-X sequence motif that, in proteasome activators, opens the 20S proteasome entry pore [ 4 ].

1. The proteasome: a proteolytic nanomachine of cell regulation and waste disposal. Biochim. Biophys. Acta 1695, 19-31
2. Chaperone-assisted assembly of the proteasome core particle. Biochem. Soc. Trans. 38, 29-33
3. Molecular mechanisms of proteasome assembly. Nat. Rev. Mol. Cell Biol. 10, 104-15
4. A conserved 20S proteasome assembly factor requires a C-terminal HbYX motif for proteasomal precursor binding. Nat. Struct. Mol. Biol. 18, 622-9