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Team:Tokyo Tech/Genetic toggle switch to implement rewritable function
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Genetic toggle switch to implement rewritable function
In order to implement rewritable function, we tried to construct Pressure Inducible Genetic Toggle Switch (in short PIGTS). We have to think two types of model - genetic circuit model and mathematical model - so as to construct PIGTS.
Genetic circuit model
1. Writable function
- Plac is induced under 30MPa pressure(PL is weakly induced)
- Express CI and GFP
- CI represses PL and causes low LacI concentration
- Express increasingly CI and GFP ⇒ Bright!!
2. Erasable function
- PL is induced by heat
- Express LacI and LacI represses Plac
- Therefore, GFP expression decreases
Mathematical model
We used two differential equation models and we call them 'room pressure model' and '30MPa pressure model'. The kinetics of the genetic toggle switch is calculated from 'room pressure model' under room pressure while that is calculated from '30MPa pressure model' under 30MPa pressure. In order to implement rewritable function. We thought to use the difference of nullclines of each system so as to satisfy the following condition
- Converge to high CI concentration state under 30MPa pressure (writable)
- Bistable under ordinary pressure (erasable)
To implement rewritable function, we had to identify the domain of appropriate parameters.
Identify the domain of appropriate parameters
Two systems have six parameters. We have already known β30Plac = 94.0 and nPL = 3.0 from earlier studies, and we identified nPlac = 2.15 by our activity determination. And we can adjust promoter - RBS strength, so we had just consider the ratio of αPlac and αPL. Therefore, we can fix αPlac.
We identified β30PL = 1.42. Therefore, we can implement rewritable function if we choose PL - RBS strength between about 0.8 and 2.5 times stronger than Plac - RBS strength.
