Making sense of the COP9 signalosome - a regulatory protein complex conserved from Arabidopsis to human

The COP9 signalosome, once defined as a repressor complex of light-activate d development in Arabidopsis, has recently been found in humans and is prob ably present in mast multicellular organisms, The COP9 signalosome is close ly related to the lid sub-complex of the 26S proteasome in structural compo sition and probably shares a common evolutionary ancestor. A multifaceted r ole of the COP9 signalosome in cell-signaling processes is hinted at by its associated novel kinase activity, as well as the involvement of its subuni ts in regulating multiple cell-signaling pathways and cell-cycle progressio n. The molecular genetic studies in Arabidopsis suggest that the complex fu nctions as part of a highly consented regulatory network, whose physiologic al role in animals remains to be determined.