Interaction of BlaI, the repressor for the beta-lactamase gene of Bacillus licheniformis, with the blaP and blaI promoters.

BlaI repressor for the beta-lactamase gene (blaP) of Bacillus licheniformis 749, was shown to repress expression of blaP and of the repressor gene (blaI), using the purified protein in a DNA-directed in vitro translation assay. Binding of BlaI to the promoter regions of blaP and blaI was examined by equilibrium and competitive binding assays. BlaI binds to the blaP promoter with an equal or only slightly higher affinity than to the blaI promoter. DNase I footprinting shows that BlaI binds directly to the blaP and blaI promoters, such that RNA polymerase binding and/or transcript elongation would be blocked.