InterPro domain: IPR033008

COP9 signalosome complex subunit 1 (CSN1) is an essential component of the COP9 signalosome complex (CSN), an eight-subunit protein complex that is found in all eukaryotes [ 1 ]. The CSN complex cleaves the isopeptide bond of ubiquitin-like protein Nedd8 from cullins and is involved in various cellular and developmental processes, such as repression of photomorphogenesis in plants and protein subcellular localization, DNA-damage response, and NF-kappaB activation in mammals [ 2 , 3 ]. CSN1 carries a C-terminal PCI (for Proteasome, COP9 signalosome, and Initiation factor 3) domain which mediates protein-protein interactions within the complex [ 4 ]. Its N-terminal domain is critical for the function of CSN [ 5 ].

1. Symmetrical modularity of the COP9 signalosome complex suggests its multifunctionality. Structure 17, 31-40
2. The devil is in the details: comparison between COP9 signalosome (CSN) and the LID of the 26S proteasome. Curr. Genet. 110, 11845-50
3. Crystal structure and versatile functional roles of the COP9 signalosome subunit 1. Proc. Natl. Acad. Sci. U.S.A. 38, 539-46
4. The Arabidopsis COP9 signalosome subunit 7 is a model PCI domain protein with subdomains involved in COP9 signalosome assembly. Plant Cell 20, 2815-34
5. TSA1 interacts with CSN1/CSN and may be functionally involved in Arabidopsis seedling development in darkness. J Genet Genomics