Dynamic interplay between antagonistic pathways controlling the sigma 32 level in Escherichia coli

Area of Science:

• Molecular Biology
• Bacterial Physiology
• Stress Response

Background:

• The heat-shock response in Escherichia coli is crucial for survival under thermal stress.
• This response is regulated by the heat-shock sigma factor, sigma32, encoded by the rpoH gene.
• Sigma32 levels increase due to enhanced synthesis and stabilization, but the mechanisms for its decrease during adaptation were unclear.

Purpose of the Study:

• To investigate the translational regulation of sigma32 synthesis during heat shock in E. coli.
• To clarify the reasons for the apparent shutoff of sigma32 synthesis during the adaptation phase of the heat-shock response.
• To elucidate the role of protein stability in regulating sigma32 levels.

Main Methods:

• Utilized a reporter system with translational coupling to assess rpoH translation.
• Employed short pulse labeling (15 s) to measure synthesis rates.
• Determined the stability of sigma32 at elevated temperatures.

Main Results:

• Heat-induced synthesis of sigma32 does not cease at the translational level.
• The apparent shutoff of sigma32 synthesis was not observed with short pulse labeling.
• Sigma32 exhibits extreme instability at 42°C (t(1/2) = 20 s), significantly contributing to its rapid turnover.
• Dynamic changes in sigma32 stability, rather than translational repression, account for the observed decrease in its levels.

Conclusions:

• The regulation of sigma32 levels during the heat-shock response is primarily driven by rapid protein degradation.
• Chaperone-mediated autogenous control significantly modulates sigma32 turnover.
• This intricate balance between rpoH translation and sigma32 degradation maintains cellular homeostasis under thermal stress.