Quantitative parameters of bacterial RNA polymerase open-complex formation, stabilization and disruption on a consensus promoter.

Transcription initiation is the first step in gene expression, and is therefore strongly regulated in all domains of life. The RNA polymerase (RNAP) first associates with the initiation factor $\sigma$ to form a holoenzyme, which binds, bends and opens the promoter in a succession of reversible states. These states are critical for transcription regulation, but remain poorly understood.