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. CSN12 forms a complex with THP3 that is recruited to transcribed genes and required for transcription elongation. 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 RRI1/CSN5, CSN9, RRI2/CSN10 and CSI1. Interacts with SEM1 and THP3. Present with 1510 molecules/cell in log phase SD medium. Belongs to the CSN12 family.