This PAC2 (Proteasome assembly chaperone) family of proteins is found in bacteria, archaea and eukaryotes. Proteins in this family are typically between 247 and 307 amino acids in length. These proteins function as a chaperone for the 26S proteasome. The 26S proteasome mediates ubiquitin-dependent proteolysis in eukaryotic cells. A number of studies including very recent ones have revealed that assembly of its 20S catalytic core particle is an ordered process that involves several conserved proteasome assembly chaperones (PACs). Two heterodimeric chaperones, PAC1-PAC2 and PAC3-PAC4, promote the assembly of rings composed of seven alpha subunits [4].

1: beta-Subunit appendages promote 20S proteasome assembly by overcoming an Ump1-dependent checkpoint. Li X, Kusmierczyk AR, Wong P, Emili A, Hochstrasser M; EMBO J. 2007;26:2339-2349. PMID:17431397

2: 20S proteasome assembly is orchestrated by two distinct pairs of chaperones in yeast and in mammals. Le Tallec B, Barrault MB, Courbeyrette R, Guerois R, Marsolier-Kergoat MC, Peyroche A; Mol Cell. 2007;27:660-674. PMID:17707236

3: A heterodimeric complex that promotes the assembly of mammalian 20S proteasomes. Hirano Y, Hendil KB, Yashiroda H, Iemura S, Nagane R, Hioki Y, Natsume T, Tanaka K, Murata S; Nature. 2005;437:1381-1385. PMID:16251969

4: PACemakers of proteasome core particle assembly. Ramos PC, Dohmen RJ; Structure. 2008;16:1296-1304. PMID:18786393