Simulation of a negative auto-regulation system with or without time delay.

<p>(A) When the simulation of the system without time delay is performed, the curves from the deterministic equations and the classic Gillespie method are smooth and approximately equal. The protein (monomer) copy number of a time series is generated from the deterministic equations (ODE, yellow curve), the classic Gillespie method (Gillespie, blue curve) and our stochastic algorithm (<i>GeneCircuits</i>, red curve). The curve of <i>GeneCircuits</i> is slightly higher than those of the two other simulations. (B) Oscillations in the protein concentration are induced at a longer time delay (1000 seconds).