Transcription regulation at the core: similarities among bacterial, archaeal, and eukaryotic RNA polymerases.

Multisubunit RNA polymerases are complex protein machines that require a specificity factor for the recognition of a specific transcription start site. Although bacterial σ factors are thought to be quite different from the specificity factors employed in higher organisms, a comparison of the σ/RNA polymerase structures with recent structures of eukaryotic Pol II together with TFIIB highlights significant functional similarities. Other work reveals that both bacterial and eukaryotic promoters are composed of modular elements that are used in different combinations. Bacteria, archaea, and eukaryotes also utilize similar strategies to alter core promoter specificity, from specificity factor exchange to the employment of activators that bind close to or overlap core promoter sequences, directing the transcriptional machinery to a new start site. Here we examine the details of core promoter recognition in bacteria that reveal the transcriptional similarities throughout biology.