From 2006.igem.org

Cell-See-Us Thermometer

This construct can be viewed in the Registry at BBa_J5530.

The functionality of the Cell-See-Us thermometer is based on the dimerization of a temperature sensitive LacI protein (BBa_J06501). This protein is produced in dimer form, which exists in equilibrium with its tetramer form. Modifying the environmental temperature (ie. of the cellular host) will cause a noticeable shift in this equilibrium.

At low temperatures, there is a high ratio of LacI ts tetramers to dimers. In the thermometer construct, the tetrameric form of the LacI binds to and represses the pLac promoter. This prevents the transcription of the tetR gene. In turn, the lack of tetR protein production will allow the pTet promoter immediately downstream to upregulate the expression of green fluorescent protein (GFP). At the same time, the second pLac in the construct will also be repressed, and since it drives monomeric red fluorescent protein (mRFP) production, there will be a decrease in intracellular levels of mRFP. The amount of GFP produced relative to the amount of mRFP will result in net green fluorescence.

Conversely, when cells containing the thermometer are exposed to high temperatures, LacI will predominately exist in the dimer form. With a lower intracellular concentration of tetramers, repression of the pLac promoters is relieved. The first pLac will cause tetR to be expressed, which will bind to and repress the pTet promoter controlling GFP expression. The second pLac will promote the transcription and

arabinose (test results: see Testing page)

==

At low temperatures, there are a large number of tetramers. These tetramers repress pLac, thus decreasing the production of monomeric red fluorescent protein (mRFP) and tetR. The reduction of tetR allows for the production of green fluorescent protein (GFP).

Conversely, at high temperatures, there is a decrease in the number of tetramers. This relieves the repression on mRFP and tetR. tetR then goes on to repress the formation of GFP. Therefore, there is a net production of mRFP.

Consequently, at high temperatures, red fluorescence dominates whereas at low temperature green will dominate.