COP9 signalosome revisited: a novel mediator of protein degradation

The COP9 signalosome is an evolutionarily conserved multiprotein complex th at was first identified as an essential complex that represses light-regula ted development in Arabidopsis. The COP9 signalosome has similarity to the lid of the 19S regulatory particle of the 26S proteasome and has recently b een shown to interact with SCF-type E3 ubiquitin ligases. Although its prec ise role in the process of protein degradation remains to be established, t he COP9 signalosome is a positive regulator of E3 ubiquitin ligases that fu nctions at least in part by mediating the deconjugation of the NEDD8/RUB-mo dification from the cullin subunit of SCF-type E3 complexes. Here,we discus s these recent findings, which add an additional component to the biology o f substrate-specific protein degradation.