InterPro domain: IPR000717

The PCI (for Proteasome, COP9, Initiation factor 3) domain (sometimes alsoreferred to as the PINT domain, for Proteasome subunits, Int-6, Nip-1, andTrip-15) is present in six different subunits of 26 proteasome lid, COP9signalosome (CSN) and eukaryotic translation initiation factor-3 (eIF3)complexes, as well as in subunits of certain other multiprotein complexes. ThePCI domain mediates and stabilizes protein-protein interactions within thecomplexes. The role of the PCI domains is most likely that of a scaffold forthe other complex subunits and other binding partners. The PCI domain couldplay a role as a universal binding domain supporting intra-complexinteractions as well as recruitments of additional ligands [ 1 , 2 , 3 , 4 , 5 , 6 ].

PCI is an ~190-amino acid domain, not well conserved in its primary sequence,usually located near the C terminus of the protein. It does not contain anyinvariant residues or any conserved pattern of charged residues that wouldsuggest a catalytic activity. The PCI domain is comprised of two subdomainsthat are intimately connected, an N-terminal helical bundle (HB) subdomain anda C-terminal globular winged helix (WH) subdomain. The C-terminal half of the PCI domain is much better conserved than the N-terminalhalf [ 7 , 7 , 7 ].

1. The PCI domain: a common theme in three multiprotein complexes. Trends Biochem. Sci. 23, 204-5
2. Homologues of 26S proteasome subunits are regulators of transcription and translation. Protein Sci. 7, 1250-4
3. Prediction of a common structural scaffold for proteasome lid, COP9-signalosome and eIF3 complexes. BMC Bioinformatics 6, 71
4. Crystal structure and versatile functional roles of the COP9 signalosome subunit 1. Proc. Natl. Acad. Sci. U.S.A. 110, 11845-50
5. Crystal structure of human eIF3k, the first structure of eIF3 subunits. J. Biol. Chem. 279, 34983-90
6. The Arabidopsis COP9 signalosome subunit 7 is a model PCI domain protein with subdomains involved in COP9 signalosome assembly. Plant Cell 20, 2815-34