SCF ubiquitin ligases control various processes by marking regulatory proteins 
for ubiquitin-dependent proteolysis. To illuminate how SCF complexes are 
regulated, we sought proteins that interact with the human SCF component CUL1. 
The COP9 signalosome (CSN), a suppressor of plant photomorphogenesis, associated 
with multiple cullins and promoted cleavage of the ubiquitin-like protein NEDD8 
from Schizosaccharomyces pombe CUL1 in vivo and in vitro. Multiple 
NEDD8-modified proteins uniquely accumulated in CSN-deficient S. pombe cells. We 
propose that the broad spectrum of activities previously attributed to CSN 
subunits--including repression of photomorphogenesis, activation of JUN, and 
activation of p27 nuclear export--underscores the importance of dynamic cycles 
of NEDD8 attachment and removal in biological regulation.