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Molecular and Cellular Biology, February 2008, p. 1404-1412, Vol. 28, No. 4
0270-7306/08/$08.00+0     doi:10.1128/MCB.01787-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Genome-Wide Analysis Identifies MYND-Domain Protein Mub1 as an Essential Factor for Rpn4 Ubiquitylation{triangledown}

Donghong Ju, Xiaogang Wang, Haiming Xu, and Youming Xie*

Barbara Ann Karmanos Cancer Institute and Department of Pathology, Wayne State University School of Medicine, 110 E. Warren Avenue, Detroit, Michigan 48201

Received 28 September 2007/ Returned for modification 5 November 2007/ Accepted 26 November 2007

The proteasome homeostasis in Saccharomyces cerevisiae is regulated by a negative feedback circuit in which the Rpn4 transcription factor upregulates the proteasome genes and is rapidly degraded by the proteasome. Previous work has identified Ubr2 and Rad6 as the cognate E3 and E2 enzymes for Rpn4 ubiquitylation. However, our recent attempts to ubiquitylate Rpn4 using purified Ubr2 and Rad6 proteins in a reconstitution system have been unsuccessful, suggesting that an additional factor is required for Rpn4 ubiquitylation. Here, we screened the entire collection of the single-gene-deletion yeast mutants generated by the Saccharomyces Genome Deletion Project and identified the mub1{Delta} mutant defective in ubiquitin-dependent degradation of Rpn4. An in vitro reconstitution ubiquitylation assay confirms that Mub1 is the missing factor for Rpn4 ubiquitylation. We further show that Mub1 directly interacts with Ubr2 and Rpn4. The MYND domain of Mub1 may play an important role in Rpn4 ubiquitylation. Interestingly, Mub1 itself is a short-lived protein and its degradation is dependent on the Ubr2/Rad6 ubiquitin ligase. Together, these data suggest that Mub1 and Ubr2 cooperate to transfer ubiquitin to Rpn4 from Rad6 and that Mub1 may switch from a partner to a substrate of the Ubr2/Rad6 ubiquitin ligase.

* Corresponding author. Mailing address: Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, 110 E. Warren Ave., Detroit, MI 48201. Phone: (313) 578-4319. Fax: (313) 831-7518. E-mail: xiey{at}karmanos.org

{triangledown} Published ahead of print on 10 December 2007.

Molecular and Cellular Biology, February 2008, p. 1404-1412, Vol. 28, No. 4
0270-7306/08/$08.00+0     doi:10.1128/MCB.01787-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Barth, S., Edlich, F., Berchner-Pfannschmidt, U., Gneuss, S., Jahreis, G., Hasgall, P. A., Fandrey, J., Wenger, R. H., Camenisch, G. (2009). Hypoxia-inducible Factor Prolyl-4-hydroxylase PHD2 Protein Abundance Depends on Integral Membrane Anchoring of FKBP38. J. Biol. Chem. 284: 23046-23058 [Abstract] [Full Text]  
  • Wang, X., Xu, H., Ju, D., Xie, Y. (2008). Disruption of Rpn4-Induced Proteasome Expression in Saccharomyces cerevisiae Reduces Cell Viability Under Stressed Conditions. Genetics 180: 1945-1953 [Abstract] [Full Text]  


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