Part:BBa_K1555000
The copa promoter wth a gfp reporter
This part is our testing part.The copa is one of the candidates of our copper sensor.For comparing with other two sequences,marO（BBa_K1555001） and cueo（BBa_K1555002）,we linked it with a reporter(BBa_E0840).With the concentration of copper rises, the expression of downstream gfp coding gene increases.We designed two experiments to test those candidates' sensitivity and specificity individually by measuring fluorescence intensity.
Sequence and Features
- 10COMPATIBLE WITH RFC[10]
- 12COMPATIBLE WITH RFC[12]
- 21COMPATIBLE WITH RFC[21]
- 23COMPATIBLE WITH RFC[23]
- 25COMPATIBLE WITH RFC[25]
- 1000INCOMPATIBLE WITH RFC[1000]Illegal BsaI.rc site found at 914
Improvement of NAU-CHINA-2016 iGEM team--Kejian Shi
Experimental Design
Overview
CopA, the principal copper effluxATPase in Escherichia coli, is induced by elevated copper in the medium.[1] CopA promoter is active in the presence of copper ion.We intended to character copA promoter independently. Therefore , we utilized RiboJ which was placed between promoter and protein coding sequence to eliminate the interference of two different parts. Output ( fluorescence) depended only on the activity of copA promoter when be induced, and not the sequence at the part junction. RiboJ can reliably maintain relative promoter strengths.
First experiment:
We test copA promoter in BL21（DE3）,DH5α. By measuring fluorescence intensity in cells by flow cytometer,we got data to analyze sensitivity and specificity of copA promoter.
Results:
In our experiment, copA promoter was induced by different concentration of copper ion (37.5umol/L、50umol/L、62.5umol/L、75umol/L) . That fluorescence intensity in cell increase firstly and decreasewith small oscillations.（Fig.3A,B） At 4-5th hour fluorescence intensity in cell increases dramatically. Dose response curves was fitted to twice induction within 9 hours. CopA promoter has relative leaky basal expression by comparing the negative control’s output and basal leakage of copA promoter in E. coli expression systems(Fig.4). In comparison of two graphs A、B, we can obviously find that the degradation of protein is much faster in DH5α than that in BL21（DE3），because BL21（DE3 ） has a deficiency of protease. In the group of 0μmol/L Cu2+, the fluorescence shows a trend of falling firstly then rising（Fig.3C）. Actually, the fluorescence which produced by the leakage of copA will not change. The change quantity comes from the different growth periods of the E.coli. We added 40ul bacterial fluid into new medium with inductionto start measuring. So bacteria will go through a period of growing from growth period to maturation period, so as to the change of the fluorescence.Maturation period is great period for the expression of protein.
Second experiment:
We placed insulator RiboJ between copA promoter and RBS.(Fig.5)
Result:
We use 50μmol/L copper ion to induce copA promoter.A device without RiboJ has an unstable Fluorescent quantity. At fourth hour, the fluorescence intensity in cells rose sharply. By contrast,a device with RiboJ response to copper ion and express GFP gradually. (Fig 6A) In addition,a device without RiboJ has high leakage with fluctuation. However, a device with RiboJ has low and stable leakage. (Fig 6B)
Improvement: We concluded that RiboJ helps reduce the leakage of copA promoter greatly. After adding copper ions, the expression of green-fluorescent protein increased steadily. So, copA promoter with RiboJ can balance the expression of target protein in Escherichia coli.
Reference: [1] Outten FW, Outten CE, Hale J, O'Halloran TV. Transcriptional activation of an Escherichia coli copper efflux regulon by the chromosomal MerR homologue, cueR. Journal of Biological Chemistry 2000;275:31024-9.
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