Noise Contributions in an Inducible Genetic Switch: A Whole-Cell Simulation Study
Figure 2
Overview of the lac genetic circuit in E. coli.
(A) In the absence of inducer, the lac repressor (LacI) binds to the lac operator preventing transcription of genes in the lac operon. (B) Following an increase in the extracellular inducer concentration, inducer enters the cell via both diffusion across the membrane and active transport by lactose permease (LacY). Once inside, inducer binds free LacI molecules preventing them from binding to the operator. (C) After the intracellular inducer concentration reaches a threshold, any bound repressor is “knocked-off” the operator leading to expression of the lac genes. (D) At high intracellular inducer concentrations the genes for lactose metabolism are fully induced. (E) After inducer is removed, repressor rebinds to the operator preventing further expression of the lac operon and the enzymes for lactose metabolism are either degraded or diluted through cellular division.