Characterization of DinR, the Bacillus subtilis SOS repressor

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Bacillus subtilis activates the SOS regulon in response to DNA damage and natural competence.
• The DinR protein is hypothesized to be the repressor of this system, analogous to E. coli LexA.
• Structural comparisons reveal conserved motifs in DinR homologs, suggesting roles in autocatalysis and varying DNA binding specificities.

Purpose of the Study:

• To experimentally validate the hypothesis that DinR functions as the cellular repressor of the B. subtilis SOS regulon.
• To characterize the biochemical properties of the DinR protein, including its autocatalytic activity and DNA binding capabilities.

Main Methods:

• Overexpression, purification, and biochemical characterization of the B. subtilis DinR protein.
• In vitro analysis of DinR autocleavage, including pH-dependent and RecA-mediated reactions.
• Electrophoretic mobility shift assays (EMSAs) to assess DinR binding to SOS box DNA sequences.

Main Results:

• B. subtilis DinR exhibits autocatalytic cleavage at the Ala91-Gly92 bond, similar to E. coli LexA, particularly at alkaline pH.
• The autocleavage reaction can be facilitated in vitro by E. coli RecA protein under physiological conditions.
• EMSAs confirmed DinR specifically binds to the characterized B. subtilis recA gene SOS box, with binding abolished by single base-pair mutations.

Conclusions:

• The findings strongly support DinR as the repressor of the SOS regulon in Bacillus subtilis.
• DinR's function and regulation share similarities with LexA in E. coli, highlighting conserved mechanisms in bacterial DNA repair.
• Specific DNA binding of DinR to SOS boxes is crucial for regulating the SOS response in B. subtilis.