Table 2.

Comparison of theory and simulation for a gene acted on by a repressor

η	Simulation	Theory
ηtot	0.51  ± 0.02	0.51
ηint	0.45  ± 0.02	0.44
ηext	0.24  ± 0.03	0.26

There are two extrinsic variables: time and the repressor. Noise is calculated for protein numbers, not concentrations. To find the intrinsic noise, two copies of the (repressed) gene were simulated (see text). All proteins (including the repressor) were created according to the full scheme of Fig. 1 (with, for simplicity, the same rate constants, although different t_ds). Parameter values are given in the supporting information, except k₀ = 0.01 s⁻¹, f̂₁ = 5 × 10⁷M⁻¹⋅s⁻¹, b₁ = 0.33 s⁻¹, and t_d = 0.7T for the repressor gene. η_rep is calculated to be 0.17 by integrating Eq. 17 over one cell cycle. Because of the repressor, expression is reduced to about 10% of its constitutive level (the expression level of Table 1). Values given are mean results from 100 simulations, and errors are ±1 SD.