Difference between revisions of "Team:Bielefeld-CeBiTec/Composite Part"

We designed this system to test as many siRNAs as possible with a high sample throughput. To achieve this, we constructed expression vectors which allow comparable expressions of different siRNAs, as well as a target vector which grants easy measurement of the silencing effectivity of a given siRNA. It is important to make all expressed siRNAs comparable to each other. Therefore we designed four Biobricks featuring the same promoter to establish the same expression rate for all siRNAs. As a first Generation, we designed the four Biobricks BBa_K2638701, BBa_K2638702, BBa_K2638758 and BBa_K2638759 (Figure 1-4) for our expression vectors. They contain a Golden Gate Assembly (GGA) cassette which can be cut out using the restriction enzyme BbsI. So it is possible to replace the whole GGA cassette with a specific siRNA with the usage of our GGA protocol. The transcription of the siRNA is terminated by the strong Terminator BBa_B0015 to make sure that all expression processes are completely terminated. While the Biobrick BBa_K2638701(Figure 1) is supposed to transcribe an siRNA without further modifications, the Biobrick BBa_K2638702 (Figure 2) also includes the Hfq binding sequence originating of the MicC-siRNA (Chen et al., 2004). The Biobrick BBa_K2638758 (Figure 3) contains the 5’-UTR from ompA as a protective sequence upstream of the siRNA insertion site and the Biobrick BBa_K2638759 (Figure 4) with both features surrounding the insertion site as well as sequences combined to add further functions to the siRNA.

Therefore, we can choose one of these explained expression vectors to be the first part of the complete TACE-system. The second part of our TACE system is a target vector, pTale, which transcribes one specific mRNA. The chosen mRNA should be silenced by the constructed siRNAs using one of the described Biobricks above. To get the optimal conditions for measuring the silencing effect of our siRNA we scheduled and constructed two Generations of target vectors. For the first generation of the target vectors we used two different Reporter Proteins: the chromoprotein AmilCp (BBa_K592009) and the blue fluorescent protein BFP (BBa_K592100). Additionaly feature the target Biobrick a linker between the GGA cassette and the reporter protein. This way, the inserted target mRNA forms a CDS fusion with the reporter protein without losing any function. If the mRNA is destroyed, no reporter protein is formed. This results in no measurement of the BFP fluorescents which is proportional to the silencing strength of the siRNA. The Target Vectors were cloned with 4 different linkers (GGGGS, BBa_K2638721; EAAAK, BBa_K2638722<(a>; XP, BBa_K2638723; cMyc, BBa_K2638724), so users of this System can choose the perfect linker for their own system. The structure of the first generation of pTale is shown in Figure 5.

The results presented in figures 7 and 8 show that the cells were growing very slowly in the 12 h of measurement time owing to the oxygen limited culture conditions in the 96 well plate used. In Figure 7 a significant increase in the Fluorescence of BFP was visible, but no noteworthy increase in the Fluorescence signal of GFP was detectable. Sequencing showed that only 50 BP of the GFP were inserted into the Target vector, explaining the missing fluorescence signal. Though it could not be shown that our system works with larger protein fusions, we were able to show that our vector works as expected with short target sequences. Vice versa, in Figure 8 a strong GFP signal was detectable, while no BFP was produced. Possibly the larger GFP protein keeps the BFP from folding correctly or inhibits the fluorophore formation in another way. Both figures show a strong increase in Fluorescence upon induction with ahTc. This confirms that the strain is producing the TetR repressor, but not on a level that is high enough to repress the promotor. Possibly the copy number of pSb1C3 proved to be too high, so that not enough TetR was abundant.
Next, we tried to clone the Guide vectors into competent cells containing the target vectors shown above. As the cells were constantly expressing GFP, we were not able to perform the blue white screening following the Golden Gate Assembly, and therefore were not able to test the pTale vectors in combination with the pGuide vectors. We were however able to clone the pGuide Biobricks into a pSB1K3 plasmid which had its native origin of replication (ori) replaced with a synthetic one (BBa_K2638751) made from parts of Team Vilnius 2017. We were able to grow cells containing that vector and sequence the ori.
As we ran out of time, we were not able to perform further tests on these vectors.