Team:ETH Zurich/project/overview/implementation
From 2014.igem.org
The XOR gate present on the third plasmid comprises an asymmetric transcription terminator flanked by two pairs of opposing recombination sites recognised by ΦC31 and Bxb1 respectively. gfp and luxI (or lasI) genes are adjacent to the XOR gate and under control of the same promoter. In the absence of both integrases, the terminator blocks transcription. Expression of either integrase alone inverts the DNA encoding the terminator and allows transcription of luxI (or lasI) and gfp. Presence of both integrases inverts the terminator twice bringing it back to its original orientation. Thus, transcription is blocked again[9].
Colonies of such cells are placed in a grid in a 3D-printed millifluidic chip. Each colony can exist in one of two states - ON and OFF. The cells are OFF if they do not produce any GFP and LuxI (or LasI) and ON when they produce GFP and LuxI (or LasI). The LuxI or LasI expressed catalyse the production of the corresponding AHL molecules which diffuse out and are propagated to the colonies in the next row. Each colony updates its state by integrating signals from its neighbours (colonies in the previous rows). We expect to see complex fluorescent patterns, such as the Sierpinski triangles, after several rows of colonies on the grid have updated their states.