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Molecular and Cellular Biology, November 2000, p. 7845-7852, Vol. 20, No. 21
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The Abundance of Met30p Limits SCFMet30p Complex Activity and Is Regulated by Methionine Availability

Dechelle B. Smothers,1 Lukasz Kozubowski,1 Cheryl Dixon,1 Mark G. Goebl,2 and Neal Mathias1,*

Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, Louisiana,1 and Department of Biochemistry and Molecular Biology and the Walther Oncology Center, Indiana University School of Medicine, Indianapolis, Indiana2

Received 28 April 2000/Returned for modification 8 June 2000/Accepted 14 August 2000

Ubiquitin-mediated degradation plays a crucial role in many fundamental biological pathways, including the mediation of cellular responses to changes in environmental conditions. A family of ubiquitin ligase complexes, called SCF complexes, found throughout eukaryotes, is involved in a variety of biological pathways. In Saccharomyces cerevisiae, an SCF complex contains a common set of components, namely, Cdc53p, Skp1p, and Hrt1p. Substrate specificity is defined by a variable component called an F-box protein. The F- box is a ~40-amino-acid motif that allows the F-box protein to bind Skp1p. Each SCF complex recognizes different substrates according to which F-box protein is associated with the complex. In yeasts, three SCF complexes have been demonstrated to associate with the ubiquitin-conjugating enzyme Cdc34p and have ubiquitin ligase activity. F-box proteins are not abundant and are unstable. As part of the SCFMet30p complex, the F-box protein Met30p represses methionine biosynthetic gene expression when availability of L-methionine is high. Here we demonstrate that in vivo SCFMet30p complex activity can be regulated by the abundance of Met30p. Furthermore, we provide evidence that Met30p abundance is regulated by the availability of L-methionine. We propose that the cellular responses mediated by an SCF complex are directly regulated by environmental conditions through the control of F-box protein stability.

* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, 1501 Kings Highway, Shreveport, LA 71130. Phone: (318) 675-8216. Fax: (318) 675-5180. E-mail: pmathi{at}lsumc.edu.

Molecular and Cellular Biology, November 2000, p. 7845-7852, Vol. 20, No. 21
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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