In vitro binding affinity of the Bacillus subtilis AbrB protein to six different DNA target regions.

AbrB is a transcriptional regulator of many Bacillus subtilis genes. A number of AbrB-binding sites have previously been delimited by DNase I footprinting studies, but the heterogeneity of the protected sequences and sizes has not led to a determination of a possible consensus motif for recognition. We have examined the affinity of AbrB for binding to six known target regions when the regions were placed in DNA fragments of various sizes. The sites are shown to vary dramatically in AbrB-binding affinity when they are present in smaller fragments, but the differences are smaller when the affinities of larger fragments are compared. Additional observations that indicate that AbrB binding may be a multistep cooperative process are reported.