AAA+ molecular machines: firing on all cylinders.
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ATPases Associated with Diverse Cellular Activitie↗
Biomedical subjects
Sarah E Ades
Publications and source records attributed to Sarah E Ades.
Growth phase-dependent regulation of the extracytoplasmic stress factor, sigmaE, by guanosine 3',5'-bispyrophosphate (ppGpp).
The sigma subunit of procaryotic RNA polymerases is responsible for specific promoter recognition and transcription initiation. In addition to the major sigma factor, sigma 70, in Escherichia coli, which directs most of the transcription in the cell, bacteria possess multiple, alternative sigma factors that direct RNA polymerase to distinct sets of promoters in response to environmental signals. By activating an alternative sigma factor, gene expression can be rapidly reprogrammed to meet the needs of the cell as the environment changes. Sigma factors are subject to multiple levels of regulation that control their levels and activities. The alternative sigma factor sigmaE in Escherichia coli is induced in response to extracytoplasmic stress. Here we demonstrate that sigmaE can also respond to signals other than extracytoplasmic stress. sigmaE activity increases in a growth phase-dependent manner as a culture enters stationary phase. The signaling pathway that activates sigmaE during entry into stationary phase is dependent upon the alarmone guanosine 3',5'-bispyrophosphate (ppGpp) and is distinct from the pathway that signals extracytoplasmic stress. ppGpp is the first cytoplasmic factor shown to control sigmaE activity, demonstrating that sigmaE can respond to internal signals as well as signals originating in the cell envelope. ppGpp is a general signal of starvation stress and is also required for activation of the sigmaS and sigma 54 alternative sigma factors upon entry into stationary phase, suggesting that this is a key mechanism by which alternative sigma factors can be activated in concert to provide a coordinated response to nutritional stress.
DNA-Directed RNA Polymerases↗
Proteolysis: Adaptor, adaptor, catch me a catch.
The ClpXP protease of bacteria can degrade a wide variety of proteins while maintaining remarkable substrate selectivity. New work in Escherichia coli implicates adaptor proteins in enhancing substrate selectivity and regulating the flow of substrates to cellular proteases.
Carrier Proteins↗
Control of the alternative sigma factor sigmaE in Escherichia coli.
Signal transduction pathways that communicate information from the cell envelope to the cytoplasm of bacteria are crucial to maintain cell envelope homeostasis. In Escherichia coli, one of the key pathways that ensures the integrity of the cell envelope during stress and normal growth is controlled by the alternative sigma factor sigmaE. Recent studies have elucidated the signal transduction pathway that activates sigmaE in response to misfolded outer membrane porins. Unfolded porins trigger the degradation of the sigmaE-specific antisigma factor RseA by the sequential action of two inner membrane proteases, leading to release of sigmaE from RseA, and induction of the stress response. This mechanism of signal transduction, regulated intramembrane proteolysis, is used in transmembrane signaling pathways from bacteria to humans.
Escherichia coli↗
Regulation of the alternative sigma factor sigma(E) during initiation, adaptation, and shutoff of the extracytoplasmic heat shock response in Escherichia coli.
The alternative sigma factor sigma(E) is activated in response to stress in the extracytoplasmic compartment of Escherichia coli. Here we show that sigma(E) activity increases upon initiation of the stress response by a shift to an elevated temperature (43 degrees C) and remains at that level for the duration of the stress. When the stress is removed by a temperature downshift, sigma(E) activity is strongly repressed and then slowly returns to levels seen in unstressed cells. We provide evidence that information about the state of the cell envelope is communicated to sigma(E) primarily through the regulated proteolysis of the inner membrane anti-sigma factor RseA, as the degradation rate of RseA is correlated with the changes in sigma(E) activity throughout the stress response. However, the relationship between sigma(E) activity and the rate of degradation of RseA is complex, indicating that other factors may cooperate with RseA and serve to fine-tune the response.
Adaptation, Physiological↗