THE TRANSCRIPTIONAL ACTIVATOR PROTEIN FIS - DNA INTERACTIONS AND COOPERATIVE INTERACTIONS WITH RNA-POLYMERASE AT THE ESCHERICHIA-COLI RRNB P1 PROMOTER

The E. coli rrnB P1 promoter owes its strength, in part, to the transc riptional activator protein FIS. FIS binds to three sites upstream of the RNA polymerase (RNAP) binding site and increases transcription in vivo four to ten-fold. In this report, hydroxyl radical and DMS footpr inting analyses show that FIS binds to its three sites along one side of the DNA helix, and that FIS bound at the promoter-proximal site (si te I) and RNAP bound at the promoter are in close proximity The bindin g of FIS at site I and RNAP at the promoter are mutually cooperative. These observations support a model for direct interaction between the FIS protein bound at site I and RNAP in transcription activation at rr nB P1. We also find that FIS does not bind cooperatively to its three sites upstream of rrnB P1, and that the relatively small activation as sociated with FIS bound at sites II and III does not result indirectly by facilitation of binding of FIS to site I.