The role of the sigma subunit in promoter recognition by RNA polymerase.

Prokaryotic transcription initiation factor sigma is required for sequence-specific promoter recognition by RNA polymerase holoenzyme. Genetic and physiological studies have indicated that sigma interacts with promoter DNA sequences but biochemical analysis did not demonstrate DNA binding by the sigma subunit itself. We have investigated both the DNA binding properties and the regulation of DNA binding for several sigma factors using partial polypeptides. In this report we demonstrate that partial sigmas can bind to promoter DNA in the absence of the core subunits of RNA polymerase and the binding is regulated by an N-terminal inhibitory domain.