Component of the COP9 signalosome complex (CSN), a complex involved in various cellular and developmental processes. The CSN complex is an essential regulator of the ubiquitin (Ubl) conjugation pathway by mediating the deneddylation of the cullin subunits of SCF-type E3 ligase complexes, leading to decrease the Ubl ligase activity of SCF-type complexes such as SCF, CSA or DDB2. The complex is also involved in phosphorylation of p53/TP53, c-jun/JUN, IkappaBalpha/NFKBIA, ITPK1 and IRF8, possibly via its association with CK2 and PKD kinases. CSN-dependent phosphorylation of TP53 and JUN promotes and protects degradation by the Ubl system, respectively. Has some glucocorticoid receptor-responsive activity. Stabilizes COP1 through reducing COP1 auto-ubiquitination and decelerating COP1 turnover rate, hence regulates the ubiquitination of COP1 targets. Component of the CSN complex, composed of COPS1/GPS1, COPS2, COPS3, COPS4, COPS5, COPS6, COPS7 (COPS7A or COPS7B), COPS8 and COPS9 isoform 1 (PubMed:18850735, PubMed:26456823). In the complex, it probably interacts directly with COPS2, COPS4, COPS5, COPS7 (COPS7A or COPS7B) and COPS9 isoform 1 (PubMed:11337588, PubMed:26456823). Interacts with the translation initiation factor EIF3S6 (PubMed:12220626). Interacts weakly with RBX1 (PubMed:11337588). Directly interacts with COP1 and 14-3-3 protein sigma/SFN (PubMed:21625211). Interacts with ERCC6 (PubMed:26030138). (Microbial infection) Interacts with the HIV-1 protein Vpr. (Microbial infection) The interaction with HIV-1 Vpr protein possibly leads its translocation to a perinuclear region. Widely expressed. Belongs to the peptidase M67A family. CSN6 subfamily. Although related to the peptidase M67A family, it lacks the JAMM motif that probably constitutes the catalytic center and therefore it probably does not have a protease activity. Truncated N-terminus.