Team:Tsinghua-A/Project/Design

Project Design

We decide to start our project with the conversion of the two basic logic gates: the And gate and the Or gate. Below are the truth tables of these two gates. So we quickly see the difference lies in the outputs when only one of the inputs is true. In the And gate if there are only one input true, either A or B, the output is false. But in the Or gate it’s to the contrary. So if we can control the output when only one input is true, we can successfully make the switch between the And gate and the Or gate.

We accomplish the design of the switch between the two gates with the help of the site-specific recombination system.
Cre-Lox system is a typical kind of site-specific recombination system. The system consists of two components: Cre recombinase and LoxP site. It is a site-specific recombinase technology widely used to carry out excisions, insertions, translocations and inversions in the DNA of cells. It allows the DNA modification targeted to a specific cell type or be triggered by a specific external stimulus.
We make use of the cre-lox site-specific system to accomplish the inversions in the DNA. When the external stimulus comes, the Cre recombinase will be expressed and then flip the sequence between the two LoxP sites.

We replace the Gene of Interest with some kind of promoter, for example, promoter A. Under the initial condition, the promoter A is able to induce the Output. But once the external signal comes, the expression of the Cre recombinase will be activated and it will lead to the flip between the two LoxP sites. Consequently, promoter A cannot bring out the output.

When it comes to the situation with 2 inputs, we make our design like this.

Between the LoxP site there’re promoter A&B and output X&Y. Initially promoter A can only induce output X, and promoter B produce output Y. Only when both promoter A&B are activated can we get the expression of output C. Definitely it serves as an And gate.
In response to the external stimulus we’ve given, the Cre recombinase come out and start the flip. After the flip either promoter A or promoter B can activate the expression of both Output X and Output Y. Then we can get output C. So the system works as an Or gate.
That’s how we construct the switch between the Add gate and the Or gate.