A novel RNA polymerase-binding protein that interacts with a sigma-factor docking site

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Genetics

Background:

• Sporulation in Bacillus subtilis is a complex process regulated by alternative RNA polymerase sigma factors.
• The protein Fin was previously identified as a negative regulator of the sporulation sigma factor σ^F.
• Loss of Fin function leads to defects in sporulation and dysregulated σ^F-directed gene transcription.

Purpose of the Study:

• To elucidate the molecular mechanism by which the Fin protein inhibits σ^F-directed gene transcription.
• To determine the direct interaction partners and binding site of Fin within the RNA polymerase complex.
• To differentiate the inhibitory mechanism of Fin from classical anti-sigma factors.

Main Methods:

• Pull-down assays to identify protein interactions.
• Chemical crosslinking to map protein binding sites.
• Bacterial two-hybrid assays to confirm protein-protein interactions.
• Nuclear magnetic resonance (NMR) chemical shift analysis to characterize Fin-RNA polymerase interactions.

Main Results:

• Fin directly binds to the RNA polymerase, specifically to the coiled-coil region of the β' subunit.
• The binding of Fin to the β' subunit is mutually exclusive with the binding of the σ^F sigma factor.
• Evidence suggests Fin acts as a competitive inhibitor, distinct from anti-sigma factors.

Conclusions:

• Fin inhibits σ^F-directed transcription by competing with σ^F for binding to the RNA polymerase β' subunit.
• This mechanism represents a novel mode of sigma factor regulation in bacterial sporulation.
• Understanding Fin's function provides insights into the intricate regulatory networks governing bacterial differentiation.