USTC/LogicGates
From 2007.igem.org
TODO
Our main design is about a Half Adder. The so-called half adder comprises two one-bit inputs and two one-bit outputs. Inside a half adder are two core devices: an XOR Gate and an AND Gate the output of which are respectively the Sum and Carry of the two inputs. The following is a truth table of a Half Adder. File:Half adder.jpg
The XOR Gate needs two inputs. Considering the feasibility and convenience of the realization, we decide that the Input Devices should be two chemical sensors rather than light sensors. A Lux promoter and a Tet promoter are applied respectively to monitor the level of AHL and aTc in the working environment. The two promoters will not be activated when neither of their inducers are present. If we add AHL to the system, it will relieve the inhibition effect of the Lux Repressor and let the system put out to the following XOR Gate the Pops signal of the lac repressor(R1). Similarly, when aTc is present in the system, we can get the Pops signal of R2 to the XOR Gate.
The figure above shows the basic structure of our input device. It functions to convert chemical signals to the PopS (the flow of RNA Polymerase molecules along DNA) signals of R1 and R2, which are actually the wires of our system.
The XOR Gate needs two inputs. Considering the feasibility and convenience of the realization, we decide that the Input Devices should be two chemical sensors rather than light sensors. A Lux promoter and a Tet promoter are applied respectively to monitor the level of AHL and aTc in the working environment. The two promoters will not be activated when neither of their inducers are present. If we add AHL to the system, it will relieve the inhibition effect of the Lux Repressor and let the system put out to the following XOR Gate the Pops signal of the lac repressor 1. Similarly, when aTc is present in the system, we can get the Pops signal of lac repressor 2 to the XOR Gate.
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Above is a figure of the XOR Gate we design. We use two operons in reverse direction. And their promoter regions are overlapped. The operator sites of the two promoter regions will receive Pops signals of two different repressors. Repressor 1 will bind to Operator 1, and Repressor 2 will bind to Operator 2. The so-called Repressor 1 and Repressor 2 can be the lac repressors mentioned above.
The two operons can be relatively isolated, and we can study one of them in detail. Take operon 1 for example. In the first situation, A1 is absent. No matter whether A2 is present or not, the transcription process will not be activated and there will not be any downstream protein to be produced. This process can be described in a digital way as shown in the following figure, and the output is Boolean false.
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In the second situation, when A1 is present and A2 is absent, the transcription process will be activated by A1 and will not be blocked A2, and the whole process will go on, thus producing the downstream protein. The whole process can be digitally described as the figure below, and the result is Boolean true.
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In the third situation, both A1 and A2 are present. The transcription process will be activated by A1, but unfortunately blocked by A2. We can read the process in a digital way shown in the figure below, and the result will be Boolean false.
The AND Gate comes directly from the Biobricks registry. It is based on the model of synergistic co-activation. The promoter can be induced by CI and lacR, and only when CI and lacR are both present will the promoter be pretty active. In all the other situations, the promoter will have only very low activity.
