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IPTG is an inducer which binds to LacI.
LacI is a repressor that is constitutively expressed. It binds to the promoter preventing the promoter from expressing an output, in this case GFP.
In the absence of IPTG, LacI is constitutively expressed. Hence the constitutive expression model from the previous characterisation step can be assumed. At the same time, it can bind to the promoter to repress it.
| Evolution of LacI concentration | Evolution of promoter concentration |  |  |
The repressor only binds to the promoter when it is in its unbound form.
| Evolution of the promoter-LacI complex | Evolution of GFP |  |  |
dGFP[GFP] is the basal rate of GFP. This is caused by the leakiness of the LacI-PLac complex when LacI does not repress the promoter completely.
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