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Nedd8-modification of Cul1 is promoted by Roc1 as a Nedd8-E3 ligase and regulates its stability.

SCF is a ubiquitin ligase and is composed of Skp1, Cul1, F-box protein, and Roc1. The catalytic site of the SCF is the Cul1/Roc1 complex and RING-finger protein Roc1. It was shown earlier that when Cul1 was co-expressed with Roc1 in Sf-9 cells in a baculovirus protein expression system, Cul1 was highly neddylated in the cell, suggesting that Roc1 may function as a Nedd8-E3 ligase. However, there is no direct evidence that Roc1 is a Nedd8-E3 in an in vitro enzyme system. Here we have shown that Roc1 binds to Ubc12, E2 for Nedd8, but not to Ubc9, E2 for SUMO-1 and Roc1 RING-finger mutant, H77A, did not bind to Ubc12. In in vitro neddylation system using purified Cul1/Roc1 complex expressed in bacteria, Roc1 promotes neddylation of Cul1. These results demonstrate that Roc1 functions as a Nedd8-E3 ligase toward Cul1. Furthermore, Roc1 and Cul1 were ubiquitinylated in a manner dependent on the neddylation of Cul1 in vitro. In addition, Cul1 was degraded through the ubiquitin-proteasome pathway, and a non-neddylated mutant Cul1, K720R, was more stable than wild-type in intact cells. Thus, neddylation of Cul1 might regulate SCF function negatively via degradation of Cul1/Roc1 complex.

Pubmed ID: 12565873


  • Morimoto M
  • Nishida T
  • Nagayama Y
  • Yasuda H


Biochemical and biophysical research communications

Publication Data

February 7, 2003

Associated Grants


Mesh Terms

  • Animals
  • Catalytic Domain
  • Cell Cycle Proteins
  • Cell Line
  • Cullin Proteins
  • Enzyme Stability
  • Humans
  • Ligases
  • Multienzyme Complexes
  • Peptide Synthases
  • Recombinant Fusion Proteins
  • SKP Cullin F-Box Protein Ligases
  • Ubiquitin
  • Ubiquitin-Protein Ligases
  • Ubiquitins