The anti-sigma factor SpoIIAB forms a 2:1 complex with sigma(F), contacting multiple conserved regions of the sigma...

Area of Science:

• Bacterial developmental biology
• Molecular mechanisms of gene regulation
• Protein-protein interactions

Background:

• Sigma(F) is a sigma-70 family RNA polymerase sigma factor crucial for Bacillus subtilis development.
• The anti-sigma factor SpoIIAB negatively regulates sigma(F) by forming an inactive complex.
• ATP binding significantly enhances SpoIIAB's interaction with sigma(F).

Purpose of the Study:

• To elucidate the structural and functional characteristics of the SpoIIAB-sigma(F) complex.
• To determine the stoichiometry and interaction interfaces within the complex.
• To understand the mechanism of sigma(F) inhibition and protection by SpoIIAB.

Main Methods:

• Gel filtration chromatography
• Dynamic light-scattering
• Analytical ultracentrifugation
• Limited proteolysis with N-terminal sequencing
• Electrospray mass spectrometry
• Deletion analysis
• Homolog investigation (Bacillus stearothermophilus)
• Co-expression in Escherichia coli

Main Results:

• The SpoIIAB-sigma(F) complex has a stoichiometry of SpoIIAB(2):sigma(F)(1).
• Sigma(F) is rapidly degraded by trypsin alone but is protected within the SpoIIAB complex.
• Protease cleavage data suggests SpoIIAB interacts with multiple conserved regions of sigma(F).

Conclusions:

• SpoIIAB binding inhibits sigma(F) activity and protects it from proteolysis.
• The interaction involves extensive contacts between SpoIIAB and conserved regions of sigma(F).
• This study provides molecular insights into the regulation of bacterial developmental transcription factors.