Fig 4.
Global feedback in a gene cascade. (a) Schematic representation of a two-gene cascade with both single-gene circuits within the feedback path such that kR1 = kRmax1/[1 + (p2/kd1)n] and kR2 = kRmax2/[1 + (kd2/p1)n]. (b) The calculated and simulated noise PSD for the circuit in a both with and without (i.e., kR1 = constant) feedback. The calculations were performed by using Eq. A-1 and A-2 from Appendix. The parameters for this circuit are as follows: krmax1 = krmax2 = 0.0231/s, b1 = b2 = 13, γp1 = γp2 = 0.0001925/s, γR1 = γR2 = 0.00578/s, kd1 = kd2 = 350, n1 = n2 = 7. For the no feedback case, kR1 was set to a constant value of 0.00449/s, giving the same value of 〈p2〉, 490, for both feedback and no feedback cases, allowing direct comparison of the PSDs. The simulation method is described in Appendix.