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Molecular and Cellular Biology, February 2000, p. 1382-1393, Vol. 20, No. 4
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The SCFHOS/beta -TRCP-ROC1 E3 Ubiquitin Ligase Utilizes Two Distinct Domains within CUL1 for Substrate Targeting and Ubiquitin Ligation

Kenneth Wu, Serge Y. Fuchs, Angus Chen, Peilin Tan, Carlos Gomez, Ze'ev Ronai, and Zhen-Qiang Pan*

Derald H. Ruttenberg Cancer Center, The Mount Sinai School of Medicine, New York, New York 10029-6574

Received 6 August 1999/Returned for modification 15 September 1999/Accepted 15 November 1999

We describe a purified ubiquitination system capable of rapidly catalyzing the covalent linkage of polyubiquitin chains onto a model substrate, phosphorylated Ikappa Balpha . The initial ubiquitin transfer and subsequent polymerization steps of this reaction require the coordinated action of Cdc34 and the SCFHOS/beta -TRCP-ROC1 E3 ligase complex, comprised of four subunits (Skp1, cullin 1 [CUL1], HOS/beta -TRCP, and ROC1). Deletion analysis reveals that the N terminus of CUL1 is both necessary and sufficient for binding Skp1 but is devoid of ROC1-binding activity and, hence, is inactive in catalyzing ubiquitin ligation. Consistent with this, introduction of the N-terminal CUL1 polypeptide into cells blocks the tumor necrosis factor alpha-induced and SCF-mediated degradation of Ikappa B by forming catalytically inactive complexes lacking ROC1. In contrast, the C terminus of CUL1 alone interacts with ROC1 through a region containing the cullin consensus domain, to form a complex fully active in supporting ubiquitin polymerization. These results suggest the mode of action of SCF-ROC1, where CUL1 serves as a dual-function molecule that recruits an F-box protein for substrate targeting through Skp1 at its N terminus, while the C terminus of CUL1 binds ROC1 to assemble a core ubiquitin ligase.

* Corresponding author. Mailing address: Derald H. Ruttenberg Cancer Center, The Mount Sinai School, of Medicine, One Gustave L. Levy Place, New York, NY 10029-6574. Phone: (212) 659-5500. Fax: (212) 849-2446. E-mail: ZQ_Pan{at}SMTPlink.mssm.edu.

Molecular and Cellular Biology, February 2000, p. 1382-1393, Vol. 20, No. 4
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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