Bacterial RNA polymerase can retain σ ⁷⁰ throughout transcription

Significance In all kingdoms of life, gene transcription is not carried out by RNA polymerase enzymes alone. Instead, the behavior of RNA polymerases during transcription initiation, elongation, and termination is regulated by accessory proteins that bind to the polymerase molecule. Bacterial σ proteins are historically thought of as transcription initiation factors primarily involved in promoter recognition. Here, we use light microscopy to directly observe the behavior of individual fluorescently labeled σ 70 subunits during transcript elongation by Escherichia coli RNA polymerase. We show that σ 70 can be retained on an RNA polymerase molecule throughout transcription and alters polymerase behavior during transcript elongation.