From 2007.igem.org
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Projects
Tri-stable Toggle Switch
The Tri-stable Toggle Switch will be able to produce three distinct, continuous (stable) outputs for each of the three inputs. A chemical will induce the system to "lock into" one state while repressing the other two states.
The Tri-stable Toggle Switch Architecture
Our three constructs are pBAD->LacI->TetR, pLacI->AraC->TetR, and pTet->AraC->LacI, where [http://en.wikipedia.org/wiki/Bcl-2-associated_death_promoter AraC] represses pBAD, [http://en.wikipedia.org/wiki/Lac_repressor LacI] represses pLac and [http://en.wikipedia.org/wiki/Tetracycline_controlled_transcriptional_activation TetR] represses pTet. The three chemicals ([http://en.wikipedia.org/wiki/Arabinose arabinose], [http://en.wikipedia.org/wiki/IPTG IPTG] and [http://en.wikipedia.org/wiki/Tetracycline Tetracycline], respectively), cause conformational changes in their respective repressor proteins which leads to gene expression. For example, in the presence of arabinose, AraC cannot repress pBAD so LacI and TetR are produced which in turn repress pTet and pLac.
AraC/BAD
Dimer structure with arabinose on the left (yellow)
The left image shows the araC dimer repressing transcription, while the right conformation enables transcription
The gene AraC one of several genes (AraA, AraB, AraD, etc) originally for the metabolism of arabinose.[http://www.mun.ca/biochem/courses/3107/Topics/Ara_operon.html] The protein forms a dimer in with and without arabinose but the structural change activates or represses the pBAD ([http://en.wikipedia.org/wiki/Bcl-2-associated_death_promoter Bcl-2-associated death promoter], an apoptotic regulator in humans).
LacI
Image[http://www.mun.ca/biochem/courses/3107/Topics/Lac_genetics.html]. LacI forms a tetramer and represses pLac. However, an inducer, such as IPTG, causes a conformation change that removes LacI from the operator site.
TetR
Tetracycline is an antibiotic
