The COP9 signalosome (CSN) is composed of eight distinct subunits and is highly homologous to the lid sub-complex of the 26S proteasome.
CSN was initially defined as a repressor of photomorphogenesis in Arabidopsis, and it has now been found to participate in diverse cellular and developmental processes in various eukaryotic organisms.
Recently, CSN was revealed to have a metalloprotease activity centered in the CSN5/Jab1 subunit, which removes the post-translational modification of a ubiquitin-like protein, Nedd8/Rub1, from the cullin component of SCF ubiquitin E3 ligase (i.e., de-neddylation).
In addition, CSN is associated with de-ubiquitination activity and protein kinase activities capable of phosphorylating important signaling regulators.
The involvement of CSN in a number of cellular and developmental processes has been attributed to its control over ubiquitin-proteasome-mediated protein degradation.
THE COP9 SIGNALOSOME
Annual Review of Cell and Developmental Biology
Vol. 19: 261-286 (Volume publication date November 2003)
First published online as a Review in Advance on June 20, 2003
Ning Wei and Xing Wang Deng