Dissection of the Bacillus subtilis spoOE binding site for the global regulator AbrB reveals smaller recognition elements.

AbrB is a global transcriptional regulator of many genes that are expressed as Bacillus subtilis exits from active growth into stationary phase and sporulation. Previous results have suggested that binding of abrB at some promoters involves multiple sites of recognition and is a cooperative process. It is shown here that the binding site at spoOE can be subdivided into 5' and 3' halves, each capable of directing AbrB binding. In addition, the central portion of the intact site can promote AbrB binding. Examination of various heterologous and homologous tandem combinations of the half-sites confirms that the native site is a complex array of overlapping suboptimal sites, the precise arrangement of which is required for optimal AbrB binding. Other data suggest that binding of multiple AbrB units is needed for stable complex formation. A binding mechanism involving numerous steps of intermediate affinity is envisioned.