The Spo0A protein of Bacillus subtilis inhibits transcription of the abrB gene without preventing binding of the polymerase to the promoter.

Repression of transcription of the abrB gene is essential to expression of many of the postexponential genes in Bacillus. The repression is due to the activity of the response regulator protein Spo0A. We have used in vitro transcription and DNase I and hydroxyl radical footprinting to explore the mechanism of transcription inhibition. Spo0A binds to specific DNA sequences (0A boxes), and two such boxes are found downstream of the tandem promoters for the abrB gene. The data indicate that both RNA polymerase and Spo0A bind simultaneously to a DNA fragment containing the promoters and the 0A boxes. The Spo0A prevents the polymerase from inducing DNA strand denaturation at the promoter for the abrB gene.