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Team:British Columbia/pBAD
From 2009.igem.org
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Arabinose sensor: the pBAD promoter
Overview
In order to make an analog biosensor, we need our traffic light to produce distinct, unique responses to a range of concentrations of an input. However, the Registry is lacking in variable strength inducible promoters. We designed two variants of the pBAD promoter, one weaker and one stronger than wild type, based on AraC binding experiments performed by Niland et al.
We did the following:
- Mutagenesis of pBAD promoter sequence to create a stronger promoter (Strong pBAD) and a weaker promoter (Weak pBAD).
- Quantification of mutant promoter-driven RFP fluorescence.
- BioBrick submission.
pBAD Mutagenesis
Above is a sequence alignment of our promoter variants with the wild type pBAD, truncated for space. For the full sequences, see our pBAD strong BBa_K206000 and pBAD weak BBa_K206001.
Quantification
We assembled each promoter with the RFP reporter part
We have been able to successfully show that at low arabinose concentrations, the activity of the Strong pBAD promoter and Weak pBAD promoter following arabinose induction is, as expected, greater and lesser respectively then the Wild Type pBAD promoter. By examining the development of a RFP reporter, it is observed that the Strong pBAD promoter has both a faster rate of development and reaches a higher maximum value compared to the Wild Type sequence. Similarly, the Weak pBAD promoter develops slower and to a lower maximum intensity.
The three promoter activites were then tested using various arabinose concentrations and the data was fit to a hill equation. It is observed that Strong pBAD and Weak pBAD are more and less responsive respectively to arabinose then the Wild Type promoter. Therefore, they could be suitable to be used in conjunction as a bio-sensor.
BioBrick Submission
Here you can find our pBAD strong BBa_K206000 and pBAD weak BBa_K206001.
