Figure 1.

(a) The oscillator has an activator–repressor motif with the σ₂₈ and C1 serving as activator and repressor, respectively. Critical to the functioning of the oscillator is the competitive binding between the two sigma factors to the core RNAP to form their respective holoenzymes. (b) Schematic representation of the σ₂₈-oscillator. The network topology comprises three DNA constructs: P₇₀-σ₂₈, P₂₈-C1-ssra, and P₇₀-deGFP. The σ₇₀ binds to the RNAP to form the RNAP-σ₇₀ holoenzyme, which binds to the P₇₀ promoter and initiates the expression of σ₂₈ and deGFP. σ₂₈ competitively binds to RNAP to form the RNAP-σ₂₈ holoenzyme, which binds to the P₂₈ promoter and initiates the expression of C1-ssra. C1-ssra exclusively binds to the P₇₀ promoter and represses the production of σ₂₈ and deGFP.