Sigma70Faktor

Sigma70Faktor, often referred to as the sigma-70 factor or σ70, is a bacterial transcription factor that directs RNA polymerase to promoter sequences to initiate transcription. In many bacteria, including Escherichia coli, it serves as the primary sigma factor responsible for transcription of housekeeping genes during exponential growth. The Sigma70Faktor family is broadly conserved across bacteria, though its exact prominence and regulation can vary by species.

Function and mechanism: The Sigma70Faktor forms a holoenzyme with the RNA polymerase core enzyme, enabling promoter recognition. It binds promoter elements located at the -35 and -10 regions, guiding the open complex formation and helping RNA polymerase start transcription. The protein comprises several functional domains, commonly described as regions 1.1 to 4.2, with region 2.4 interacting with the -10 element and region 4.2 with the -35 element. In free form, region 1.1 can inhibit nonspecific DNA binding, and promoter binding relieves this inhibition to allow transcription initiation.

Regulation and coordination: Sigma70Faktor activity is modulated by growth conditions and cellular priorities. It competes with alternative sigma factors for access to the RNA polymerase core enzyme; under stress or stationary phase, sigma factors such as σS (sigma S) or others can redirect transcription toward stress-related genes. Anti-sigma factors and regulatory proteins further fine-tune Sigma70Faktor availability and activity.

Importance and applications: The Sigma70Faktor is essential for viability in many bacteria and serves as a key reference point for studying promoter architecture and transcription initiation. It is also a focus in biotechnology and synthetic biology for controlling baseline gene expression and understanding bacterial transcriptional regulation.