Fig 3. Power spectral densities.

Normalized power spectral density of the fluctuations of repressor obtained by averaging 8000 periodograms from stochastic simulations of Fig 2 (black dots), and the approximate normalized power spectral density computed by using Eq (4) (red curve). $\widehat{\omega }$ indicates the peak frequency, and Δω is the difference of the two frequencies at which the power takes the 90% of the peak value. The frequency ω is given in radians per minute (rad min⁻¹).