What is a Genetic Toggle Switch?
What is a Genetic Toggle Switch?
A genetic toggle switch is a type of genetic circuit coding for a repressor protein. This repressor prevents the expression of another gene, allowing the expression of a protein to be linked to the activity of different genetic circuit. 1 Toggle switches can be used to introduce logic to cells, and have major roles in cell differentiation and decision making.
Two genetic toggle switches can be used to find equilibria, by encoding repressors for each other's promoters - these are called bistable gene-regulatory networks. 2 In these circuits, the transcriptional units (promoter + repressor protein) need to be orientated in opposite directions (away from each other) to prevent polymerase crashing / cross-talk between the units (see figure 1, ref. 2). I think it would be possible to put these units on separate plasmids, however (reading further on ref. 2 confirms this is possible). Having genes expressed in this way gives an equilibrium of expression, which can be useful in giving 'memory' to genetic circuits. So for instance, expression levels can be maintained after removing a stimulus and then reinstating it.
Even in the presence of small disturbances, genetic toggle switches maintain constant expression levels in cells 3.
Toggle switches are also found in G-protein coupled receptors (GPCRs), linking the binding of a ligand to the activation of an intracellular catalytic process. 4