Effect of Crp on protection of the gltBDF promoter by RNAP. A fragment of gltBDF DNA from -571 to +51, labelled at the +51 end was used for DNase I protection assays. The first 4 lanes represent a sequencing ladder of the region. RNAP was used at 30 nM and Crp at 100 nM. Reactions with CRP contained 2mM cAMP.