Component of the COP9 signalosome (CSN) complex that acts as an regulator of the ubiquitin (Ubl) conjugation pathway by mediating the deneddylation of the cullin subunit of SCF-type E3 ubiquitin-protein ligase complexes The CSN complex is involved in the regulation of the mating pheromone response. Component of a COP9 signalosome-like (CSN) complex, composed of RRI1/CSN5, CSN9, RRI2/CSN10, PCI8/CSN11, CSN12 and CSI1. In the complex, it probably interacts directly with CSN9 and CSN12. Interacts also with RPN5.