Team:Cambridge/Bioluminescence/Bacterial Codon optimisation

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(Differential Expression)
(Differential Expression)
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=Differential Expression=
=Differential Expression=
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In Vibrio fischeri, LuxA and B are expressed at five times the levels of LuxC, D, E and G. Since all these genes are transcribed on the same mRNA, but have their own Ribosome Binding Sites, this is probably due to differences in codon usage [http://www.annualreviews.org/doi/pdf/10.1146/annurev.mi.42.100188.001055 (Meighen et al. 1988)]. A number of rare codons are found in Lux C, D, E and G, but not in LuxA and B. Since we did not receive the newly synthesised LuxA and B in time, we constructed a new operon using our LuxC, D, E and G, and the LuxAB BioBrick that was put into the registry by the Edinburgh iGEM team 2009 (BBa_216008). These genes originate from Xenorhabdus luminescens. Compared to Vibrio fischeri, there is only limited amino acid identity in the Lux A and B genes (52% and 66% respectively). Yet the literature describes both as using the same substrates. To use foreign genes from two very different donor species in one pathway in E.coli is an exciting test of our understanding of the processes involved in bacterial bioluminescence and of the power of synthetic biology in general.
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In ''Vibrio fischeri'', LuxA and B are expressed at five times the levels of LuxC, D, E and G. Since all these genes are transcribed on the same mRNA, but have their own Ribosome Binding Sites, this is probably due to differences in codon usage ([http://www.annualreviews.org/doi/pdf/10.1146/annurev.mi.42.100188.001055 Meighen et al. 1988]). A number of rare codons are found in Lux C, D, E and G, but not in LuxA and B. Since we did not receive the newly synthesised LuxA and B in time, we constructed a new operon using our LuxC, D, E and G, and the LuxAB BioBrick that was put into the registry by the Edinburgh iGEM team 2009 (BBa_216008). These genes originate from Xenorhabdus luminescens. Compared to ''Vibrio fischeri'', there is only limited amino acid identity in the Lux A and B genes (52% and 66% respectively). Yet the literature describes both as using the same substrates. [http://aem.asm.org/cgi/content/abstract/55/10/2607 Schmidt et al. 1989] describe positive complementation test using components from ''V. fisheri'' and ''Xenorhabdus luminescens''. To use foreign genes from two very different donor species in one pathway in E.coli is an exciting test of our understanding of the processes involved in bacterial bioluminescence and of the power of synthetic biology in general.
In this construct, LuxC, D, E and G are codon optimised, but LuxA and B are not. In order to adjust the ratio of gene expression between these genes to the state found in nature, we chose to put LuxA and B under a very strong, phage derived promoter (plambda) to be constitutively expressed. The other genes can now be put under any promoter to create a PoPS-to-light device. In conjunction with an inducible or repressible promoter, this could be used as a reporter device. To test the system, we placed the LuxCDEG under an arabinose induced pbad promoter (BBa_i0500).
In this construct, LuxC, D, E and G are codon optimised, but LuxA and B are not. In order to adjust the ratio of gene expression between these genes to the state found in nature, we chose to put LuxA and B under a very strong, phage derived promoter (plambda) to be constitutively expressed. The other genes can now be put under any promoter to create a PoPS-to-light device. In conjunction with an inducible or repressible promoter, this could be used as a reporter device. To test the system, we placed the LuxCDEG under an arabinose induced pbad promoter (BBa_i0500).

Revision as of 22:48, 24 October 2010