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

fig5-1:genetic circuit model


1. Writable function

  • Plac is induced under 30MPa pressure
  • Express CI and GFP
  • CI represses PL and causes low LacI concentration
  • Express increasingly CI and GFP(inserted destruction tags) ⇒ Bright!!


2. Erasable function

  • PL is induced by heat
  • Express LacI and LacI represses Plac
  • Therefore, GFP expression decreases


Mathematical model

fig5-2:Atmospheric pressure model. It is known that nPL = 3.0 from earlier studies, and we identified nPlac = 2.15 by our activity determination.
fig5-3:30MPa pressure model

We used two differential equation models and we call them 'atmospheric pressure model' and '30MPa pressure model'. In order to implement rewritable function, we decided 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 atmospheric pressure (erasable)


fig5-4:Desirable condition. left:under atmospheric pressure (nullclines of fig:5-2), right:under 30MPa pressure (nullclines of fig:5-3).




















It is known that Plac activity under 30MPa pressure is 94.0 times stronger than Plac activity under atmospheric pressure, so, β30Plac = 94.0. If 30MPa additional activity rate of PL (β30PL) or the ratio of Plac - RBS strength (αPlac) and PL-RBS strength(αPL) are not appropriate value, we can't construct PIGTS. So we calculated the domain of appropriate β30PL and the ratio of αPlac and αPL.


fig5-5:The domain of appropriate parameters if αPlac = 3.0


We identified β30PL = 1.42 by our experiment under 30MPa pressure. Therefore, we can implement rewritable function if we choose PL - RBS strength range from 2.4 to 7.4.

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