Team:UANL Mty-Mexico/wetlab/mini project-esp

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Miniproject

Introduction


It is know that TetR (like others transcriptional repressors) can allow a basal expression. Because of that, it would be a good idea to reduce that basal expression using a molecular tool which does not cause noise to circuits and systems.

The last year our team participated with the project “Thermo coli” (Team: UANL_Mty-Mexico). The main biobrick (K1140006) that we used was composed for the fluorescent protein mCherry (E1010) regulated by the ptet promoter (R0040) and a 37°C thermometer. This year we decided to use that biobrick part to develop a mini-project. We want to proveif it is possible to enhance the repression of a gene by a combined use of the repressor protein TetR (transcriptional regulation) and a RNA thermometer (post-transcriptional regulation).

Constructions and Parts


The fluorescent part was synthetized based on the promoter ptet (R0040), a RBS fused to a RNA thermometer which was obtained on a previous work (Neupertet al, 2008), the mCherry (E1010) and the transcriptional terminator T7 (B0010-B0012).

Figure 1. This part (K1140006) changes its behavior in response to temperature variations above and below 37°C. This part is available in pUC57, pSB1C3 and pSB2K3.

Also, it was constructed a part that does not have a thermometer, so that we could see its effect on the fluorescence. This part was constructed using the same promoter (R0040) with the RFP/mCherry protein generator (K081014).

Figure 2. This part does not change its behavior in response to temperature. The biobrick part is available in pSB1C3 and pSB2K3.

We constructed TetR generatorswith different constitutive promoters. We used the promoters J23109, J23106 and J23111 with the relative force 106, 1185 and 1487, respectively.These parts have a RBS (B0034), the CDS for the TetR repressor (C0040) and the T7 transcriptional terminator (B0010-B0012). Moreover, we used the biobrick part K145201 as a positive control to expression of TetR, because it is a generator with promoter force 396. Also the RBS and transcriptional terminator are both the same.

Figure 3. The names of constructed parts are BBa_K1480003, K1480004 and K1480005. Their respective promoters are J23109, J23106 and J23111. Actually, those parts are just available in pBca.

Measurements


For the measurements, we made constructions in order to have the biobrick parts in compatible plasmids. It means that those which codifies to mCherry are in pSB2K3 and the tetR genes are in pSB1A2.
The bacteria E. coli Top10 were transformed to have the next 7 cultures:

Table 1. Combinations for clones
Fluorescent protein (in pSB2K3) TetR generator
ptet + mCherry Any
ptet + mCherry J23111 + tetR
ptet + thermometer + mCherry Any
ptet + thermometer + mCherry J23019 + tetR
ptet + thermometer + mCherry J23116 + tetR
ptet + thermometer + mCherry J23106 + tetR
ptet + thermometer + mCherry J23111 + tetR

The cultures were growth at 25 and 37°C for 15 hours. The conditions were the same as it is indicated in protocols. The wave lengths that we used were 530+/-25 (excitation) and 590+/-35 (Emission).


Results


First, we had to prove the function of our construction ptet + mCherry (K1480002). So, it was decided to prove its fluorescence with and without repressor. That TetR generator is the one has been proved before that works (K145201). The results are shown in table 2.

Table 2. Repression over K1480002.
Without repressor With repressor
3869 2590
4012 2450
4320 2296
4232 2601
3794 2564
Mean 4045.4 2500.2
SD 226.7 128.9

Figure 4. Graph of previous results.


Then, we started to prove our synthetic part (K1140006) with the set generators TetR. The results are shown in the next table.

Table 3. Repression over K1140003.
Without repressor With K1480003 With K145201 With K1480004 With K1480005
2770 852 868 731 738
2621 827 766 780 673
3294 866 1212 898 655
3492 946 1212 813 746
3038 725 742 608 450
2710 776 744 827 516
1671 620 536 566 NG*
Mean 2799.9 801.9 868.8 746.6 630.0
SD 590.9 106.3 254.7 120.6 121.1

Figure 5. Mean and SD of every set of results of table 3.

References
Neupert J, Karcher D and Bock R (2008) Design of simple synthetic RNA thermometers for temperature- controlled gene expression in Escherichia coli. Nucleic Acids Res36:e124.

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