Post‐initiation control by the initiation factor sigma

SummaryBacterial core RNA polymerase can initiate transcription at promoters only if guided by a σ subunit that directs the core enzyme to a subset of σ‐specific promoters. Specific and stable interactions between the promoter DNA elements and σ are required for efficient promoter recognition. At the same time, persistent σ‐DNA contacts can hinder RNA polymerase escape from a promoter or halt the enzyme downstream from the transcription start site, thereby reducing transcription of the affected genes. This microcommentary reviews recent data arguing that σ‐dependent stalled transcription complexes form frequently in vivo, where they likely play important and diverse regulatory roles.