Difference between revisions of "Part:BBa K819006"

Revision as of 17:17, 26 September 2012

Testing device for Luminesensor

A fast degrading GFP placed under the control of sulA promoter with a specific mutation (only recognizable by our luminesensor, not by E.coli endogenous LexA). After it is co-transformed with luminesensor plasmid into E.coli cells, illuminating the cells by blue light, the light will triger the dimerizaiton of luminesensor, making dimer bind to this promoter, thus to inhibit the transcription of the downstream GFP; if the environment is dark, the luminesensor will not dimerize and no repression of the promoter will occour.

The time course of GFP expression level controlled by luminesensor before and after optimization at 2 hour intervals for 26 hours. As shown in figure below, the GFP expression began to rise after incubating at dark for about 10 hours.

Figure.1 The time course of GFP expression level controlled by luminesensorbefore and after optimization

Luminesensor under decreasing illumination shows decreasing repression, and thereby, increasing GFP expression.

Figure.2 Photo of GFP level to the illumination time

We tested the sensitivity of luminesensor by examining the light-dependent transcriptional activity of a GFP-ssrA reporter. ssrA is a protein tag that induces fast degradation of protein, which in our case facilitated the observation of transcriptional activity.

Cells expressing luminesensor exposed to different light intensity showed manifest light-repressed reporter gene transcription. As shown in the Figure 3, all of the cells with dissimilar attenuators showed incredible repression efficiency.

It proves that once the cells are exposed to natural light, the transcription of reporter gene will be strongly repressed, although still presents as a dose response. Besides, in the negative control group, which was entirely in the dark state, the expression of GFP ran up to a high degree of 50,000. As a matter of fact, when we serially diluted light-emitting cells which expresses bacterial luciferase, the cells expressing Luminesensor presents significant dose response. Taking everything into account, our luminesensor does possess high sensitivity across several orders of magnitude.

Figure.3 Luminance measurement of different attenuator.

The response threshold value of our luminesensor, BBa_K819005, was not found simply using blue LED and attenuating filters, because the luminesensor is so sensitive to very dim light which cannot be detected by the photometer we used.(see characterization:sensitivity) And it’s difficult to control the intensity of very dim light simply using attenuating filters. So, we managed to find the threshold and therefore regulate the response intensity using bio-luminescence as light source based on our light-communication system.

Light emitting cell broth was diluted to create different light intensity, represented by the dilution ratio. (e.g. 0.001 indicates the weakest light intensity) And with this method we managed to get closer to the linear area of our sensor’s response. And we succeeded in regulating the gene expression level by changing the light intensity.

The photo below shows the GFP level to the dilution ratio of light emitting cell.

Figure 4. Photo of GFP level to the dilution ratio of light emitting cell.

References

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Sequence and Features