Two domains within σ N (σ 54 ) cooperate for DNA binding

Abstract

The σ-N (σ^N) subunit of the bacterial RNA polymerase is a sequence specific DNA-binding protein. The RNA polymerase holoenzyme formed with σ^N binds to promoters in an inactive form and only initiates transcription when activated by enhancer-binding positive control proteins. We now provide evidence to show that the DNA-binding activity of σ^N involves two distinct domains: a C-terminal DNA-binding domain that directly contacts DNA and an adjacent domain that enhances DNA-binding activity. The sequences required for the enhancement of DNA binding can be separated from the sequences required for core RNA polymerase binding. These results provide strong evidence for communication between domains within a transcription factor, likely to be important for the function of σ^N in enhancer-dependent transcription.