Premium
The cellular level of the recognition factor RssB is rate‐limiting for σ S proteolysis: implications for RssB regulation and signal transduction in σ S turnover in Escherichia coli
Author(s) -
Pruteanu Mihaela,
HenggeAronis Regine
Publication year - 2002
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2002.03123.x
Subject(s) - proteolysis , biology , sigma factor , control theory (sociology) , artificial intelligence , computer science , biochemistry , rna polymerase , control (management) , escherichia coli , enzyme , gene
Summary Degradation of the general stress sigma factor σ S of Escherichia coli is a prime example of regulated proteolysis in prokaryotes. Whereas exponentially growing cells rapidly degrade σ S , various stress conditions result in stabilization and, therefore, rapid accumulation of σ S . Proteolysis of σ S requires the response regulator RssB, a direct recognition factor with phosphorylation‐dependent affinity for σ S , which targets σ S to the ClpXP protease. Here, we demonstrate that a sudden increase in σ S synthesis results in σ S stabilization, indicating titration of an essential proteolytic component. Evidence is provided that RssB is the overall rate‐limiting factor for σ S proteolysis. As a consequence, the cell has to continuously adjust the expression of RssB to σ S in order to maintain σ S proteolysis in growing cells, despite variations in the rate of σ S synthesis. Such homeostatic feedback‐coupling is provided by rssB transcription being dependent on the σ S ‐controlled rssAB operon promoter. However, strong and rapid increases in σ S synthesis, in re‐sponse to acute stress, exceed the compensatory potential of this feedback loop with the result that σ S is stabilized because of RssB titration. We propose that RssB control of σ S proteolysis functions as a genetic switch, in which (i) the ‘off’ state (low σ S levels caused by proteolysis) is stabilized by a homeostatic negative feedback, and (ii) the threshold for switching to the ‘on’ state (high levels of stable σ S ) is dependent on the cellular level of active, i.e. phosphorylated RssB.