DISSECTION OF THE BACILLUS-SUBTILIS SPOOE BINDING-SITE FOR THE GLOBALREGULATOR ABRB REVEALS SMALLER RECOGNITION ELEMENTS

AbrB is a global transcriptional regulator of many genes that are expr essed as Bacillus subtilis exits from active growth into stationary ph ase and sporulation. Previous results have suggested that binding of A brB at some promoters involves multiple sites of recognition and is a cooperative process. It is shown here that the binding site at spo0E c an be subdivided into 5' and 3' halves, each capable of directing AbrB binding. In addition, the central portion of the intact site can prom ote AbrB binding. Examination of various heterologous and homologous t andem combinations of the half-sites confirms that the native site is a complex array of overlapping suboptimal sites, the precise arrangeme nt of which is required for optimal AbrB binding. Other data suggest t hat binding of multiple AbrB units is needed for stable complex format ion. A binding mechanism involving numerous steps of intermediate affi nity is envisioned.