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| - | <-- the following part needs to be edited; I just copied the text from the articles or just put links--> | + | <h2 class='title' style='font-size: 120%;'>Double Population Toggle Switch</h2> |
| - | <br><br>The Quorum Sensing molecules:<br><br> | + | |
| - | Acylated Homoserine Lactone (AHL)<br>
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| - | http://en.wikipedia.org/wiki/N-Acyl_homoserine_lactone<br>
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| - | Auto Inducer 1 (AI-1):<br>
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| - | · Primarily involved in intracellular communication<br>
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| - | Auto Inducer 2 (AI-2):<br>
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| - | · Primarily involved in intercellular communication<br>
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| - | <br>
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| - | From: http://aem.asm.org/content/71/11/7033.full <br>
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| - | “The type AI-1 QS regulatory system is composed of four elements: (i) a transcriptional regulator (protein family R); (ii) a cis-acting DNA palindromic sequence; (iii) an acyl-homoserine lactone (AHL), which is the signaling molecule or autoinducer (AI-1); and (iv) the AHL synthase protein (protein family I), which synthesizes the AI (6, 20, 48, 49). It is currently accepted that AI-1 diffuses freely between the cellular and external environments and complexes with the R protein only at a high cell density. The AHL-R complex binds through the R carboxyl domain to the specific site which corresponds to a palindromic sequence centered at about position −40 with respect to the transcriptional start sites of the target genes (15, 48, 49).”
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| - | <br><br>
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| - | <Show picture of how the quorum molecules work>
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| - | <br><br>
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| | + | Our double population toggle uses many of the same concepts as our single population toggle. |
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| - | <Show diagram - maybe number the diagram and number this text respectively so they go with each other?>
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| - | <br><br>
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| - | Population 1:<br>
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| - | · Positive Feedback: The oscillation sequence begins with the synthesis of LsrK. When LsrK binds with AI-2 produced by the third population, it creates a dimer that binds to the PLsrA promoter. This promotes luxl, which when bound with SAM, produces AHL. The gene for YFP is attached at the end of the Luxl gene, so that when luxl is produced, the bacterium also fluoresces yellow.<br>
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| - | · Negative Feedback: In population 1, LasR is constitutively promoted. When it binds with AI-1, it creates a dimer, binds with PLasR and promotes arac. Arac then binds with PBad to repress the production of LsrK, AHL and YFP.<br><br>
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| - | Population 2:<br> | + | INSERT Dual Population Toggle.jpg HERE |
| - | · Positive Feedback: The second population in the sequence is induced by the AHL produced by population 1. When AHL is in the presence of the bacteria, it creates a dimer with LuxR and binds to PLuxR. PLuxR then promotes LasI which when bound with SAM produces AI-1. RFP is attached to the end of the LasI gene, so that when LasI is produced, the bacterium also fluoresces red.<br>
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| - | · Negative Feedback: In population 2, LsrK is constitutively promoted. When it binds with AI-2, it creates a dimer, binds with PLsrA and promotes LacI. LacI then binds with PLac to repress the production of LuxR, AI-1 and RFP.<br><br>
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| - | Population 3:<br>
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| - | · Positive Feedback: The third population in the sequence is induced by the AI-1 produced by population 2. When AI-1 is in the presence of the bacteria, it creates a dimer with LasR and binds to PLasR. PLasR then promotes LuxS which when bound with SAM produces AI-2. CFP is attached to the end of the LuxS gene, so that when LuxS is produced, the bacterium also fluoresces red.<br>
| + | In order for either population to produce fluorescence proteins, it must be receiving a proper amount of quorum signalling molecules from the other population. When one of the populations is signalled by the other, it begins to produce fluorescence proteins along with the inhibitor proteins LacI or TetR. These proteins in turn inhibit the production of signalling molecules to be sent to the opposite population of cells. In short, either population is either fluorescing or sending a signal to the other population to fluoresce. The mechanism is controlled with the addition of IPTG or ATc in much the same way as the single population toggle. |
| - | · Negative Feedback: In population 3, LuxR is constitutively promoted. When it binds with AHL, it creates a dimer, binds with PLuxR and promotes TetR. TetR then binds with PTetR to repress the production of LasR, LuxS, and CFP.<br>
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Our double population toggle uses many of the same concepts as our single population toggle.
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