CSN5 is one of eight subunits (CSN1 to 8) of the highly conserved COP9 signalsome (CSN) complex originally identified as a regulator of light-mediated development in Arabidopsis. Characterization of CSN from yeast to mammals reveals its function as a modulator of signal transduction pathways involved in a variety of cellular and developmental processes. One of the major functions of the CSN is the regulation of protein degradation via intersection with the ubiquitin-proteasome pathway and regulation of E3-ubiquitin ligases. CSN also possesses kinase activity. CSN5 has been identified as the subunit that functions to remove Nedd8, an ubiquitin-like modifier, from cullin-based E3-ubiquitin ligases. CSN5 also functions as a coactivator of nuclear receptors. COP9 signalsome complex subunit 5, signalsome subunit 5, SGN5, jun activation domain-protein 1, COPS5, JAB1, MOV-34, MGC3149.