Design

The quorum sensing oscillator

The genetic oscillator based on quorum sensing. The luxI protein generates AHL , it’s a signal molecule. In the presence of luxR ,the complex can activate the promoter .When promoter activated ,the LuxI and AiiA express and accumulate. Because the AiiA protein can degrade the AHL and repress the promoter indirect, the expression of LuxI and AiiA are depressed, Thus forming an oscillation by the negative feedback circuit. (Danino T, et al. 2010)

Fig 1. The quorum sensing oscillator

The key point of this oscillator is that the promotor LuxpR is induced by quorum sensing molecular AHL, so the state of cells can be synchronous by communicating with each other, being convenient for us to observe and regulate the oscillator in the population level.

The dual feedback oscillator

The genetic oscillator is based on a negative feedback loop and a positive feedback loop. The hybrid promoter (Plac/ara-1) is composed of an activation operator site and a repression operator site .It is activated by the AraC protein in the presence of arabinose and repressed by LacI protein in the absence of IPTG. The araC, lacI, and GFP genes are under the control of three identical copies of the hybrid promoter thus formed three co-regulated transcriptional modules.

Fig 2. The dual feedback oscillator

The addition arabinose and IPTG will activate the promoter and result in transcription of each component of the circuit , and increased production of AraC in the presence of arabinose results in a positsive feedback loop that increase promoter activity. However the concurrent increase in production of LacI results in a linked negative feedback loop decreases promoter activity. So the concentration of the GFP would change with the variation of promoter activity.（Hasty, Jeff. 2008.）

The key point of this oscillator is that the hybrid promotor can be effected by chemical revulsive IPTG/Arabinose, so we can make the oscillator more tunable and robust by adding the chemical revulsive.

Regulation to the oscillator--the light control system

In this system , the three genes can generate a lightsensitive complex, which can phosphorylate ompR protein in dark, and the phosphorylated ompR protein will active the ompC promoter and the downstream gene can express. But in the presence of red light, the kinase activity is inhibited, resulting in repressing the promoter and inhibiting the expression of related genes.（Anselm, Levskaya, et al. 2005.）

Fig 3. The light control system

Fig 4. The genetic circuit of light control system

If the downstream genes is lacI or Arac , luxI or AiiA ,like this ,we can regulate the oscillator by the red light.

For the quorum sensing oscillator:

Fig 5.

For the dual feedback oscillator:

Fig 6.

Reference：

1. Danino T, Mondragón-Palomino O, Tsimring L, et al. A synchronized quorum of genetic clocks. [J]. Nature, 2010, 463(7279):326-330.

2. Hasty J. A fast, robust and tunable synthetic gene oscillator. [J]. Nature, 2008, 456(7221):516-519.

3. Anselm L, Chevalier A A, Tabor J J, et al. Synthetic biology: Engineering Escherichia coli to see light [J]. Nature, 2005, 438(7067):441-442.