AbrB, a regulator of gene expression in Bacillus, interacts with the transcription initiation regions of a sporulation gene and an antibiotic biosynthesis gene.

The abrB gene of Bacillus subtilis is believed to encode a repressor that controls the expression of genes involved in starvation-induced processes such as sporulation and the production of antibiotics and degradative enzymes. Two such genes, spoVG, a sporulation gene of B. subtilis, and tycA, which encodes tyrocidine synthetase I of the tyrocidine biosynthetic pathway in Bacillus brevis, are negatively regulated by abrB in B. subtilis. To examine the role of abrB in the repression of gene transcription, the AbrB protein was purified and then tested for its ability to bind to spoVG and tycA promoter DNA. In a gel mobility shift experiment, AbrB was found to bind to a DNA fragment containing the sequence from -95 to +61 of spoVG. AbrB protein exhibited reduced affinity for DNA of two mutant forms of the spoVG promoter that had been shown to be insensitive to abrB-dependent repression in vivo. These studies showed that an upstream A + T-rich sequence from -37 to -95 was required for optimal AbrB binding. AbrB protein was also observed to bind to the tycA gene within a region between the transcription start site and the tycA coding sequence as well as to a region containing the putative tycA promoter. These findings reinforce the hypothesis that AbrB represses gene expression through its direct interaction with the transcription initiation regions of genes under its control.