Difference between revisions of "Part:BBa K3788019"

Revision as of 17:33, 21 October 2021

Expression of GFP and of the timer device under the control of the LexA-controlled promoter

Induced by the SOS response (LexA dependent) upon DNA damages (UV, mitomycin…). This promoter allow the expression of the operon caa and cal. caa gene is coding for Colicin A (ColA) a toxin toxin produced by E. coli strains, and active against other non-immune E.coli strains. In this contruction GFP permit to understand the mechanism, and ColA isn't able to have his toxin activity. To protect themselfs, E. coli have an imumnity protein coded by cai gene (-). cal gene is codding for a lysis protein, when this protein is produce ColA can be delivered in the extracellular medium after the E. coli cells lysis. The regulation is complex and involves many regulatory elements: terminator (+) and (-), promoters, antisense coding sequence, etc.

Figure : schematic representation of the construction with the different coding sequences, restriction sites used to insert the GFP coding sequence, and the known terminators.

Methods

In order to characterize the promoter strength, we fused it to the GFP encoding sequence BBa_E0040 and to the timer-lysis device part BBa_K3788018 (composite part BBa_K3788019). Induction of the SOS response was induced by mitomycin C treatments and the fluorescence was recorded in a dose-dependent manner using a microplate reader. Following iGEM Measurement recommendations, the GFP fluorescence intensity was converted to a concentration of fluorescein protein thanks to a standard curve of fluorescein dilution series.

Results

Figure:Measure of the GFP signal (as fluorescein equivalent) of bacterial liquid cultures expriming BBa_K3788019 across time with different quantities of MitomycinC added to the growing medium.

The experiment was done in triplicate. Standard deviation is small and not visible on the graph.

Our data confirmed that the promoter part BBa_K3788017 responds to mitomycin in a dose dependent manner from 50 to 800 ng.ml-1. The signal is significantly detected 90 min to 130 min after the beginning of the experiment, depending of the inducer tested concentration.

Moreover, we showed that the promoter is strongly repressed in the absence of the inducer, as no fluorescence signal is detected for the untreated control during the time course of the experiment (450 min).

Finally, thanks to the composite part BBa_K3788019, we demonstrated that during the 90 to 210 min window after induction, there is a linear relationship between the accumulation of GFP signal and Mitomycin concentration. We established titration curves for this time period (R²>0.975).

Figure:Linear relationship between mitomycin concentration and GFP signal 90 and 210 minutes after induction

Sequence and Features