Component of the COP9 signalosome complex (CSN), a complex involved in various cellular and developmental processes such as photomorphogenesis and auxin and jasmonate responses. 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. It is involved in repression of photomorphogenesis in darkness by regulating the activity of COP1-containing Ubl ligase complexes. The complex is also required for degradation of IAA6 by regulating the activity of the Ubl ligase SCF-TIR complex. Regulates the TSO2 subcellular localization. May be involved in nucleic acid binding. Component of the CSN complex, probably composed of CSN1, CSN2, CSN3, CSN4, CSN5 (CSN5A or CSN5B), CSN6 (CSN6A or CSN6B), CSN7 and CSN8. In the CSN complex, it probably interacts directly with CSN4. Interacts (via PCI domain) with CSN1 (via PCI domain) and CSN8 (via PCI domain), and (via C-terminal tail) with CSN6A, TSO2 and RNR2A. Cannot interact simultaneously with CSN1 and CSN8 to form ternary complexes. Also exists as a monomeric form. Binds to the translation initiation factors TIF3E1 and TIF3H1 (PubMed:15548739, PubMed:19704582). The PCI domain is not sufficient to efficiently mediate CSN complex assembly and for biological activity. Phosphorylated. Belongs to the CSN7/EIF3M family. CSN7 subfamily.