The network of a self-regulating gene. (a) The topology of the network. A single copy of the gene in the chromosome encodes a protein transcription factor (TF), which is synthesized at the rate of s0 or s1, depending on whether the operator site is bound (state 0) or unbound (state 1). The TF binds the operator site of the gene at a rate of b. It unbinds at a rate of u. The TF is also subject to degradation at a rate of d determined by the degradation machinery. Here the symbol ∅ represent the state of being degraded. (b) The chemical reactions of the five stochastic processes and the corresponding reaction rates.