General stress response in α-proteobacteria: PhyR and beyond.
In addition to stress-specific responses, most bacteria can mount a general stress response (GSR), which protects the cells against a wide range of unspecific stress conditions. The best-understood examples of GSR are the σ(B)-cascade of Bacillus subtilis and the RpoS response in Escherichia coli. While the latter is conserved in many other proteobacteria of the ß-, γ- and δ-clades, RpoS homologues are absent in α-proteobacteria and their GSR has long been a mystery. Recent publications finally unraveled the core of the GSR in this proteobacterial class, which is mediated by EcfG-like σ-factors. EcfG activity is controlled by NepR-like anti-σ factors and PhyR-like proteins that act as anti-anti-σ factors. These unusual hybrid proteins contain an N-terminal EcfG-like domain that acts as a docking interface for NepR, and a C-terminal receiver domain typical for bacterial response regulators. Upon phosphorylation, PhyR titrates NepR away from EcfG, thereby releasing the σ-factor to recruit RNA polymerase and initiate transcription of its target genes. In this issue of Molecular Microbiology, Herrou et al. describe the function and three-dimensional structure of PhyR from Caulobacter crescentus. This structure is key to understanding the mechanism of the reversible, phosphorylation-dependent partner switching module that orchestrates the GSR in α-proteobacteria.
Department Biology I, Microbiology, Ludwig-Maximilians-University, Munich, Germany.
Anna
A
Staroń
Thorsten
T
Mascher
D020561:Alphaproteobacteria / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial; D010766:Phosphorylation; D012808:Sigma Factor / Q000235:genetics / Q000502:physiology*; D013312:Stress, Physiological
D001426:Bacterial Proteins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria