relA-dependent RNA polymerase activity in Escherichia coli

Area of Science:

• Molecular Biology
• Microbiology
• Genetics

Background:

• The relA gene product in Escherichia coli synthesizes guanosine tetraphosphate (pGpp), a key alarmone regulating the stringent response.
• Understanding the role of pGpp in modulating RNA synthesis under stress conditions is crucial for bacterial physiology.

Purpose of the Study:

• To investigate the impact of a temperature shift on RNA synthesis parameters in isogenic relA+ and relA- Escherichia coli strains.
• To elucidate the role of guanosine tetraphosphate (pGpp) and relA function in regulating rRNA and tRNA synthesis and RNA polymerase activity.

Main Methods:

• Comparative analysis of RNA synthesis parameters in isogenic relA+ and relA- Escherichia coli strains.
• Measurement of rRNA chain growth rate, rRNA stability, stable RNA gene activity, and RNA polymerase activity following a temperature shift from 30°C to 42°C.

Main Results:

• rRNA chain growth rate doubled in both strains, while newly synthesized rRNA became unstable.
• Stable RNA gene activity decreased in the relA+ strain but increased in the relA mutant.
• RNA polymerase activity significantly decreased in the relA+ strain but remained largely unchanged in the relA mutant.

Conclusions:

• rRNA gene activity and RNA polymerase activity are dependent on intracellular guanosine tetraphosphate (pGpp) concentrations.
• Altered rRNA chain elongation and stability are likely consequences of temperature or amino acid starvation, independent of relA function.