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Sigma factor displacement from RNA polymerase during Bacillus subtilis sporulation
1Department of Microbiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284-7758, USA.
Journal of Bacteriology
|August 10, 1999
Summary
Bacillus subtilis sporulation involves replacing vegetative sigma factor (sigma(A)) with sporulation sigma factors on RNA polymerase. This study shows new sigma factors displace old ones, even without transcription activity, highlighting competition for RNA polymerase.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Genetics
Background:
- During Bacillus subtilis sporulation, vegetative sigma factor (sigma(A)) is replaced by sporulation-specific sigma factors on RNA polymerase (RNAP).
- Understanding the mechanism of this sigma factor exchange is crucial for deciphering sporulation regulation.
Purpose of the Study:
- To investigate how sporulation-specific sigma factors displace the primary vegetative sigma factor (sigma(A)) from RNAP during Bacillus subtilis sporulation.
- To determine the role of sigma factor activity versus mere presence in this displacement process.
Main Methods:
- Velocity centrifugation and Western blot analyses were employed to monitor the association of RNAP with different sigma factors (sigma(A), sigma(E), sigma(K)).
- Mutant strains of Bacillus subtilis lacking or having altered sporulation sigma factors were analyzed.
Main Results:
- Sigma(A) association with RNAP decreased significantly during sporulation, from 50% at T(0) to 2-8% by T(3).
- Failure to synthesize sigma(E) or using a non-transcriptionally active sigma(E) variant resulted in higher sigma(A)-RNAP association at T(3).
- Sigma(K) is essential for displacing sigma(E) from RNAP and for the degradation of sigma(E).
Conclusions:
- The sequential presence of sporulation sigma factors on RNAP, not necessarily their transcriptional activity, drives the displacement of pre-existing sigma factors.
- Competition for RNAP binding by successive sporulation sigma factors is a key mechanism for holoenzyme transitions during Bacillus subtilis sporulation.