ARCfflTECTURE OF delta~(54)-DEPENDENT PROMOTERS: INTERPLAY BETWEEN CRP-cAMP AND P_(II)-NTR SYSTEMS FORMS A NOVEL REGULATORY NETWORK BETWEEN CARBON METABOLISM AND NITROGEN ASSIMILATION IN ESCHERICHIA COLI

摘要

The delta~(54)-RNA polymerase (Edelta~(54)) predominantly contacts one face of the DNA helix in the closed promoter complex, and interacts with the upstream enhancer-bound activator via DNA looping. By introducing protein-induced DNA bends at preciselocations between upstream enhancer sequences and the core promoter of the delta~(54)-dependent glnAp2 promoter without changing the distance in-between, we observed a strong enhanced or decreased promoter activity. The relative positioning and orientations of Edelta~(54), the DNA-bending protein, and the enhancer-bound activator on linear DNA were determined by in vitro footprinting analysis. Results provide evidence that the activator must approach the Edelta~(54)closed complexes from the unbound faceof the promoter DNA helix to catalyze open complex formation. In this case, the activator and Edelta~(54) interact face-to-face and form a complex in which promoter DNA is in between Edelta~(54) and the activator like a 'sandwich'. This is further supported by the modeling of activator-promoter DNA-Edelta~(54) complex (see Figure 1).