Contents 1 Decoy Sites 1.1 The Model 1.1.1 Decoy Sites 1.1.2 Copy Number 1.1.3 Protein Expression Rate 1.2 Simulation Result 1.3 References

Decoy Sites

To tune the level of protein expression, we used decoy sites. Decoy sites are tandem repeats of DNA where transcriptional factor can bind to but don't promote gene expression. Therefore it competes with promoter sites and lowers the gene expression rate. LeeDecoyTek-Hyung Lee and Narendra Maheshri, A regulatory role for repeated decoy transcription factor binding sites in target gene expression. Molecular Systems Biology 8, 576 (2012)

The Model

Decoy Sites

The model of decoy sites consists of two reactions, i.e., the transcriptional factor binding to decoy sites and to promoter sites. The schematic graph of this model is illustrated in . The reactions are:
$$ \eqalignno{ \ce{$T + N\,$ &<=>[\text{Kⁿ _on}][\text{Kn-off}] $TN$} & (1) \\ \ce{$T + P\,$ &<=>[\text{Kp-on}][\text{Kp-off}] $TP$} & (2) \\ }$$

The T is the transcriptional factor, which is FNR. It can binds to either the decoy sites(N) or the promoter(P). The production and degradation of T is included in the FNR model.

Copy Number

The copy numbers refers to the number of certain plasmids in E.coli. In this project we used the derivative of pBR322. So the copy number is between 15 to 20.CopyNr, Growth of Bacterial Cultures. www.qiagen.com/Knowledge-and-Support/Spotlight/Plasmid-Resource-Center/Growth%20of%20bacterial%20cultures/ , () As the plasmid has a low copy number, we take the average of copy number and multiple it with the number of promoter and decoy sites.

Protein Expression Rate

The protein expression rate was assumed to be linear to the promoter binding ratio in Tek-Hyung Lee and Narendra MaheshriLeeDecoy. As we have only one promoter in each plasmid, we have either the 'on-state' plasmid or the 'off-state' plasmid. So we take the idea of linearity and convert the assumption to that the protein expression rate is linear to the proportion of 'on-state' plasmid.

Simulation Result

The input is the concentration of FNR protein. This result is taken from the part of FNR protein and converted from micro molar concentrations to number of molecules.

The simulated result of decoy site binding ratio

The simulated result of promoter binding ratio

This would be the input for the modeling of protein generation. We assume the protein production rate is linear to the promoter binding ratio.LeeDecoy

References