Effect of transcription factor resource sharing on gene expression noise
Fig 2
A kinetic model of transcription, incorporating the TFs’ binding and unbinding to multiple competing promoters.
(A) The rate of binding of a TF to a promoter is kon and the rate of unbinding of the TF from the promoter is koff. (B) List of possible stochastic transitions leading to either formation or dissociation of ‘TF-promoter’ complexes, and their respective statistical weights. The weights represent the probability that each transition will occur during a time interval, Δt. TF copy number, promoter copy number, and the instantaneous number of complexes are denoted by NTF, NP and n respectively. (C) While an activator is bound to a promoter, it promotes the binding of RNAP molecules to the promoter, which subsequently leads to the production of an mRNA molecule at a rate r. Each mRNA molecule then decays at a rate γ. Here, m denotes mRNA copy number. The basal transcription rate, when the activator is not bound to the promoter, is assumed to be zero (see S1 Text for a more general model for activators with a nonzero basal rate). (D) List of stochastic transitions leading to changes in mRNA copy number by the action of activators and their respective weights. (E) When a repressor is bound to a promoter, it hinders RNAP binding to the promoter, subsequently blocking mRNA production. However when a promoter is not bound to any repressor molecule, it produces mRNA molecules at a rate r, which again subsequently decay at a rate γ. (F) List of stochastic transitions leading to changes in mRNA copy number by the action of repressors, with respective weights.