Part:BBa_K3989009
Quroum sensing esaS promoter: PesaS
A promoter that can interact with EsaR protein and activate downstream gene transcription.
Basic information
In contrast to PesaRC( BBa_K3989008), this promoter will down-regulate the gene expression when EsaR attaches to the esa box on it. Meanwhile, this promoter has only one esa box which is at position -60.(see figure 1)
Figure 1. Mechanism of the EsaR being an activator under the control of PesaS. The red dots are the specific AHL molecule and in our project it is 3OC6HSL[1]. When interacting with the AHL molecules, the EsaR protein will dislocate from the promoter. Thus, the PesaS will not recruit the RNA polymerase and down-regulate the transciption.
Characterisation
Together with the EsaR protein and its variants, we characterised this promoter using the same strategy. The strategy we used is to express a GFP in a plasmid(detail of the construct: BBa_K3989025) with different EsaR protein variants. The AHL molecule's concentration are same as people used in the literature[1]. We used plate reader and flow cytometry to analyse the fluorescence generated by GFP, the results are shown in figure 3 and 4.
Figure 2. Fluorescence intensity measurement by plate reader(96-well plate). The measurements were done every one hour and this is the curve of the last test.
Figure 3. Fluorescence intensity measurement by flow cytometry. The samples are taken from the plate, in which the bacteria has been cultured for 7 hours.
From the characterisation, we reproduced the results from the literature that PesaS can down-regulate the gene expression when the EsaR protein is dislocated from the esa box.
Characterization contribution made by iGEM23_SDU-CHINA
Author: Suiru Lu PesaS is a natural EsaR-activated promoter. EsaR can act as both transcriptional activator and repressor. PesaR is a natural EsaR-repressed promoter, whereas PesaS is a natural EsaR-activated promoter. At low cell density (low ρ), EsaR binds to its esa box to turn off PesaR and turn on PesaS. In the presence of AHL, EsaR can bind to AHL and release from the DNA. Thus, at high cell density(high ρ), the PesaR is turned on and the PesaS is turned off
Results
We characterized PesaS-RBS-GFP together with PesaRwt-RBS-mkate, PesaRc-RBS-mkate and PesaRp-RBS-mkate. The green curve in the figure shows the results for PesaS. PesaS expression peaks at around 4-6 h and then rapidly declines to 0 at around 8-10 h.
Reference
1) Shong, J., & Collins, C. H. (2013). Engineering the esaR promoter for tunable quorum sensing-dependent gene expression. ACS synthetic biology, 2(10), 568-575.
2) Shong, J., Huang, Y. M., Bystroff, C., & Collins, C. H. (2013). Directed evolution of the quorum-sensing regulator EsaR for increased signal sensitivity. ACS chemical biology, 8(4), 789-795.
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