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Team:Michigan/Project
From 2009.igem.org
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==<B><font size=4>Suicide Mechanism</font></B>== | ==<B><font size=4>Suicide Mechanism</font></B>== | ||
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| - | The Terminator's suicide mechanism, or kill switch, operates through the [http://partsregistry.org/wiki/index.php?title=Part:BBa_K112808<font color=navy><B>Enterobacteria phage T4 Lysis Device</B></font>] created by the Berkley 2008 team. We proposed two mechanisms for cell lysis | + | The Terminator's suicide mechanism, or kill switch, operates through the [http://partsregistry.org/wiki/index.php?title=Part:BBa_K112808<font color=navy><B>Enterobacteria phage T4 Lysis Device</B></font>] created by the Berkley 2008 team. We proposed two mechanisms for cell lysis. In the arabinose inducible suicide mechanism Pu is controlling the cell survival and in the suicide mechanism with tunable repression Pu is controlling cell death. |
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The suicide operon consists of an arabinose-dependent promoter controlling expression of the holin and endolysin proteins, followed by the Pu promoter controlling the antiholin gene shown in the figure below. This way, none of the genes are activated until the device is released into the contaminated area, along with a quantity of arabinose. This results in the arabinose-mediated expression of the lytic genes holin and endolysin, as well as the toluene-mediated expression of antiholin, which posttranslationally inhibits the lytic proteins. Then, when the toluene disappears (when it is all metabolized) from the local region of the individual device, antiholin is no longer expressed, allowing the lytic proteins to destroy the cell. | The suicide operon consists of an arabinose-dependent promoter controlling expression of the holin and endolysin proteins, followed by the Pu promoter controlling the antiholin gene shown in the figure below. This way, none of the genes are activated until the device is released into the contaminated area, along with a quantity of arabinose. This results in the arabinose-mediated expression of the lytic genes holin and endolysin, as well as the toluene-mediated expression of antiholin, which posttranslationally inhibits the lytic proteins. Then, when the toluene disappears (when it is all metabolized) from the local region of the individual device, antiholin is no longer expressed, allowing the lytic proteins to destroy the cell. | ||
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| + | <B><font size=3>Suicide Mechanism with Tunable Repression</font></B> | ||
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| + | In this design, a repression mechanism is downstream of the Pu promoter, and this this represses the production of holin and endolysin proteins. A constitutive promoter is placed in the front of the antiholin gene so antiholin is constantly produced. When toluene is present, it activates the Pu promoter which results in the repression of the promoter expressing holin and endolysin. As a result, the cell survives. However, in the absence of toluene, the repressor protein is not produced, so holin and endolysin levels rise to the point that the cells are lysed. | ||
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| + | The motivation for this design is as follows. The Berkeley 2008 design used an inducible promoter in front of the holin and endolysin; this inducible promoter then would trigger the onset of the killing mechanism. In our design, we wanted to use Pu to make the killing mechanism responsive to toluene concentration. However, we needed to set this up such that Pu would prevent cell death. Due to this requirement, we designed an inverter that is comprised of the repression module. This way, we did not have to modify the Berkeley part, which is characterized as working. | ||
Revision as of 20:58, 21 October 2009
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The Toluene TerminatorOverviewThe Toluene Terminator is a Pseudomonas device that aims to identify the toxic compound toluene in an environmental setting (e.g. a spill into soil from an underground petrol tank), move to and uptake it, metabolize it, and destroy itself when all of the toluene has been metabolized. This device will require four basic modules: toluene chemorecognition, chemotaxis, toluene metabolism, and a suicide mechanism. This year we have been working on toluene metabolism and the suicide mechanism. Toluene MetabolismThe goal of this project is to work with the toluene degrading abilities that already exist in P. putida mt-2 (ATCC 33015) on the pWW0-TOL plasmid. The pathway on this plasmid is comprised of the upper pathway where toluene is metabolized into catechol and the lower, meta-pathway where catechol is converted into acetaldehyde and pyruvate. The regulation of toluene degradation on the pWW0 plasmid is presented below.
Upper Pathway
The Pr (regulator) promoter is a constitutive promoter in P. putida mt-2 and expresses the XylR regulator protein. When there is no toluene in the system, the XylR protein acts as a repressor for Pr to prevent leaky expression. When toluene is present, the toluene binds with the XylR regulator protein to create a complex that activates the Pu (upper pathway) promoter and starts to degrade toluene. The upper pathway enzymes XylA, XylB and XylC degrade toluene into catechol. Lower Pathway
The XylR-toluene complex also activates Ps, the promoter that expresses XylS which is the protein that regulates the lower meta-pathway. XylS regulates the lower pathway Pm (meta-pathway) promoter by itself or complexed with benzoate, a product from the upper pathway. When activated Pm expresses Xyl D-L to finish degrading toluene. Sensing Toluene
Our project is aimed at characterizing the promoters in the pWW0 plasmid to sense when the toluene degrading process is finished, signaling the cell to commit suicide. The promoter we chose to sense the presence of toluene is the Pu promoter. In order to characterize this promoter we created Bba_K270003, a device that has the Pu promoter expressing GFP. To have this device function in strains other than P. putida mt-2 that already contains the XylR regulating protein, the part Bba_K270001 was created from the Pr XylR portion of the pWW0 plasmid to regulate the Pu promoter. By combining the functions of these two parts, the intensity of GFP can be used to measure the promoter activity when induced with non-lethal level of toluene. Currently, we have made the Pu GFP and Pr XylR parts. In the future, we plan on creating one device composed of these two parts and testing the Promoter activity in both E. coli and P. putida. With this data we will have a better idea of how to link the toluene sensing ability of the Pu promoter with suicide mechanism.
Suicide MechanismThe Terminator's suicide mechanism, or kill switch, operates through the [http://partsregistry.org/wiki/index.php?title=Part:BBa_K112808Enterobacteria phage T4 Lysis Device] created by the Berkley 2008 team. We proposed two mechanisms for cell lysis. In the arabinose inducible suicide mechanism Pu is controlling the cell survival and in the suicide mechanism with tunable repression Pu is controlling cell death.
The suicide operon consists of an arabinose-dependent promoter controlling expression of the holin and endolysin proteins, followed by the Pu promoter controlling the antiholin gene shown in the figure below. This way, none of the genes are activated until the device is released into the contaminated area, along with a quantity of arabinose. This results in the arabinose-mediated expression of the lytic genes holin and endolysin, as well as the toluene-mediated expression of antiholin, which posttranslationally inhibits the lytic proteins. Then, when the toluene disappears (when it is all metabolized) from the local region of the individual device, antiholin is no longer expressed, allowing the lytic proteins to destroy the cell.
Suicide Mechanism with Tunable Repression In this design, a repression mechanism is downstream of the Pu promoter, and this this represses the production of holin and endolysin proteins. A constitutive promoter is placed in the front of the antiholin gene so antiholin is constantly produced. When toluene is present, it activates the Pu promoter which results in the repression of the promoter expressing holin and endolysin. As a result, the cell survives. However, in the absence of toluene, the repressor protein is not produced, so holin and endolysin levels rise to the point that the cells are lysed. The motivation for this design is as follows. The Berkeley 2008 design used an inducible promoter in front of the holin and endolysin; this inducible promoter then would trigger the onset of the killing mechanism. In our design, we wanted to use Pu to make the killing mechanism responsive to toluene concentration. However, we needed to set this up such that Pu would prevent cell death. Due to this requirement, we designed an inverter that is comprised of the repression module. This way, we did not have to modify the Berkeley part, which is characterized as working.
Kill Switch with Tunable Repression
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