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Issue 6, 2012
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Proteolysis of beta-galactosidase following SigmaB activation in Bacillus subtilis

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In Bacillus subtilis the σB mediated general stress response provides protection against various environmental and energy related stress conditions. To better understand the general stress response, we need to explore the mechanism by which the components interact. Here, we performed experiments in B. subtilis wild type and mutant strains to test and validate a mathematical model of the dynamics of σB activity. In the mutant strain BSA115, σB transcription is inducible by the addition of IPTG and negative control of σB activity by the anti-sigma factor RsbW is absent. In contrast to our expectations of a continuous β-galactosidase activity from a ctc::lacZ fusion, we observed a transient activity in the mutant. To explain this experimental finding, we constructed mathematical models reflecting different hypotheses regarding the regulation of σB and β-galactosidase dynamics. Only the model assuming instability of either ctc::lacZ mRNA or β-galactosidase protein is able to reproduce the experiments in silico. Subsequent Northern blot experiments revealed stable high-level ctc::lacZ mRNA concentrations after the induction of the σB response. Therefore, we conclude that protein instability following σB activation is the most likely explanation for the experimental observations. Our results thus support the idea that B. subtilis increases the cytoplasmic proteolytic degradation to adapt the proteome in face of environmental challenges following activation of the general stress response. The findings also have practical implications for the analysis of stress response dynamics using lacZ reporter gene fusions, a frequently used strategy for the σB response.

Graphical abstract: Proteolysis of beta-galactosidase following SigmaB activation in Bacillus subtilis

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Supplementary files

Article information

25 Jan 2012
20 Mar 2012
First published
17 Apr 2012

Mol. BioSyst., 2012,8, 1806-1814
Article type

Proteolysis of beta-galactosidase following SigmaB activation in Bacillus subtilis

U. W. Liebal, P. K. Sappa, T. Millat, L. Steil, G. Homuth, U. Völker and O. Wolkenhauer, Mol. BioSyst., 2012, 8, 1806
DOI: 10.1039/C2MB25031D

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