Modeling Promoter Activity

Modeling Promoter Activity

In order to use synthetic promoters to their fullest potential, we have to understand how they work. Sythetic promoters cannot help us model gene circuit activity unless models are developed for the activity of the promoter itself. Determining how exactly a promoter's strength correlates to its mutations is not easy, since for the most part it requires working with promoters on the level of individual sets of nucleiotides.

Jensen and Hammer (1997): Spacer Sequences

In this 1997 paper, Jensen and Hammer constructed a library of synthetic promoters based on the Lactococcus lactis prokaryotic promoter in order to better determine how gene sequence of promoters was tied to the promoter strength. Specifically, Jensen and Hammer were looking for a way to construct a constitutively active promoter – one that was always turned on, without needing an inducer – that could be safely used to tune gene expression in industrial-scale metabolic engineering projects, where inducers might be impractical or hazardous.

In order to tune the steady-state L. lactis promoter without using an inducer, Jensen and Hammer had to create a library of L. lactis mutant promoters, all with various levels of activity. To generate the library, they used the method described in Promoters and Reporters in Synthetic Biology: constructing oligonucleiotides that matched the genes common to all previous L. lactis promoters and mutants, then allowing the oligonucleiotides to be joined together by random spacer sequences.

After the promoter library was synthesized, promoters were cloned into both L. lactis and E. coli; each cell culture containing a different promoter was tested for the level of beta-galactosidase activity.