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J. Bacteriol. doi:10.1128/JB.01233-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Clp dependent proteolysis down-regulates central metabolic pathways in glucose starved Bacillus subtilis

Institute of Microbiology, Ernst-Moritz-Arndt-University, 17487 Greifswald, Germany, Friedrich-Loeffler-Institute, Federal Research Institute for Animal Health, Boddenblick 5a, 17493 Greifswald-Insel Riems, Germany, Department of Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9751 NN Haren, The Netherlands. Department of Biochemistry, University of Illinois, 600 South Mathews, Urbana, IL 61801, USA

^* To whom correspondence should be addressed. Email: Ulf.Gerth{at}uni-greifswald.de.

	Abstract

Entry into stationary phase in Bacillus subtilis is not only linked to a re-direction of the gene expression program, but also to post-translational events such as protein degradation. Using ³⁵S-methionine pulse-chase labeling and 2D-PAGE we monitored the intracellular proteolysis pattern during glucose starvation. Approximately 200 protein spots diminished in the wild-type during an 8-hour time course. The degradation rate of at least 80 proteins was significantly reduced in clpP, clpC and clpX mutant strains. Enzymes of amino acid and nucleotide metabolism were over-represented among these Clp substrate candidates. Notably, several first committed step enzymes for biosynthesis of aromatic and branched-chain amino acids, cell wall precursors, purines and pyrimidines appeared as putative Clp substrates. Radioimmunoprecipitation demonstrated GlmS, IlvB, PurF and PyrB to be novel ClpCP targets. Our data imply that Clp proteases down-regulate central metabolic pathways upon entry into a non-growing state and thus contribute to the adaptation to nutrient starvation. Obviously, non-functional, unprotected or even "unemployed" proteins seem to be recognized and proteolyzed by Clp proteases when the resources for growth become limited.