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The response regulator RssB, a recognition factor for σ S proteolysis in Escherichia coli , can act like an anti‐σ S factor
Author(s) -
Becker Gisela,
Klauck Eberhard,
HenggeAronis Regine
Publication year - 2000
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.1365-2958.2000.01736.x
Subject(s) - proteolysis , biology , regulator , mutant , phosphorylation , microbiology and biotechnology , ubiquitin , genetics , gene , biochemistry , enzyme
σ S (RpoS) is the master regulator of the general stress response in Escherichia coli . Several stresses increase cellular σ S levels by inhibiting proteolysis of σ S , which under non‐stress conditions is a highly unstable protein. For this ClpXP‐dependent degradation, the response regulator RssB acts as a recognition factor, with RssB affinity for σ S being modulated by phosphorylation. Here, we demonstrate that RssB can also act like an anti‐sigma factor for σ S in vivo , i.e. RssB can inhibit the expression of σ S ‐dependent genes in the presence of high σ S levels. This becomes apparent when (i) the cellular RssB/σ S ratio is at least somewhat elevated and (ii) proteolysis is reduced (for example in stationary phase) or eliminated (for example in a clpP mutant). Two modes of inhibition of σ S by RssB can be distinguished. The ‘catalytic’ mode is observed in stationary phase cells with a substoichiometric RssB/σ S ratio, requires ClpP and therefore probably corresponds to sequestering of σ S to Clp protease (even though σ S is not degraded). The ‘stoichiometric’ mode occurs in clpP mutant cells upon overproduction of RssB to levels that are equal to those of σ S , and therefore probably involves binary complex formation between RssB and σ S. We also show that, under standard laboratory conditions, the cellular level of RssB is more than 20‐fold lower than that of σ S and is not significantly controlled by stresses that upregulate σ S. We therefore propose that antisigma factor activity of RssB may play a role under not yet identified growth conditions (which may result in RssB induction), or that RssB is a former antisigma factor that during evolution was recruited to serve as a recognition factor for proteolysis.