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{{Imperial/Box1|Modelling the repression of the promoter

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.

[[Image:Repression.JPG|600px]]

[[Image:Equations_plac.JPG‎|600px]]

'''Evolution of LacI concentration'''

[[Image:Conc_LacI.jpg|300px]]

The repressor only binds to the promoter when it is in its unbound form.

'''Evolution of promoter concentration'''

[[Image:Free_promoters.jpg|300px]]

'''Evolution of the promoter-LacI complex'''

[[Image:Conc_PLacI_Complex.jpg|300px]]

'''Evolution of GFP'''

[[Image:conc_FP.jpg|300px]]

d<sub>GFP</sub>[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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