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Molecular and Cellular Biology, June 2009, p. 3307-3318, Vol. 29, No. 12
0270-7306/09/$08.00+0     doi:10.1128/MCB.00240-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Polyubiquitination by HECT E3s and the Determinants of Chain Type Specificity{triangledown}

Hyung Cheol Kim and Jon M. Huibregtse*

Institute for Cellular and Molecular Biology, Section of Molecular Genetics and Microbiology, University of Texas at Austin, Austin, Texas 78712

Received 24 February 2009/ Returned for modification 17 March 2009/ Accepted 29 March 2009

Polyubiquitination can mediate several different biochemical functions, determined in part by which lysine of ubiquitin is used to link the polyubiquitin chain. Among the HECT domain ubiquitin ligases, some, such as human E6AP, preferentially catalyze the formation of K48-linked polyubiquitin chains, while others, including Saccharomyces cerevisiae Rsp5 and human Itch, preferentially catalyze the formation of K63-linked chains. The features of HECT E3s that determine their chain type specificities have not been identified. We show here that chain type specificity is a function solely of the Rsp5 HECT domain, that the identity of the cooperating E2 protein does not influence the chain type specificity, that single chains produced by Rsp5 contain between 12 and 30 ubiquitin moieties, and that the determinants of chain type specificity are located within the last 60 amino acids of the C lobe of the HECT domain. Our results are also consistent with a simple sequential-addition mechanism for polyubiquitination by Rsp5, rather than a mechanism involving the formation of either E2- or E3-linked polyubiquitin chain transfers.

* Corresponding author. Mailing address: Institute for Cellular and Molecular Biology, University of Texas at Austin, 2500 Speedway, Austin, TX 78712. Phone: (512) 232-7700. Fax: (512) 232-3432. E-mail: huibreg{at}mail.utexas.edu

{triangledown} Published ahead of print on 13 April 2009.

Molecular and Cellular Biology, June 2009, p. 3307-3318, Vol. 29, No. 12
0270-7306/09/$08.00+0     doi:10.1128/MCB.00240-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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