MOLECULAR ANATOMY OF A TRANSCRIPTION ACTIVATION PATCH - FIS-RNA POLYMERASE INTERACTIONS AT THE ESCHERICHIA-COLI RRNB P1 PROMOTER

FIS, a site-specific DNA binding and bending protein, is a global regu lator of gene expression in Escherichia coli. The ribosomal RNA promot er rrnB P1 is activated 3- to 7-fold in vivo by a FIS dimer that binds a DIVA site immediately upstream of the DNA binding site for the C-te rminal domain (CTD) of the alpha subunit of RNA polymerase (RNAP). In this report, we identify several FIS side chains important specificall y for activation of transcription at rrnB P1. These side chains map to positions 68, 71 and 74, in and flanking a surface-exposed loop adjac ent to the helix-turn-helix DNA binding motif of the protein. We also present evidence suggesting that FIS activates transcription at rrnB P 1 by interacting with the RNAP alpha CTD. Our results suggest a model for FIS-mediated activation of transcription at rrnB P1 that involves interactions between FIS and the RNAP alpha CTD near the DNA surface. Although FIS and the transcription activator protein CAP have little s tructural similarity, they both bend DNA, use a similarly disposed act ivation loop and target the same region of the RNAP alpha CTD, suggest ing that this is a common architecture at bacterial promoters.