Our biobrick, pPGK1Gx, is an improvement to pTRE(4)Gx and pTRE(2)Gx from uOttawa's 2014 project. While the previous parts were GEV-repressible but required rtTA to express, pPGK1Gx has strong, constitutive expression. This part does not require the cell to have rtTA to get a signal, and does not require the user to maintain a steady concentration of anhydrotetracycline or doxycycline to modulate the rtTA activity. This way, rtTA is free to be used as a transcription factor elsewhere in a genetic network.

Not only does this behaviour fit with achieving tri-stability, but it is also ideal for implementing new logic gates with genes. This promoter, being repressible, can be used as a single-input NOT gate with a twist. Its input may be able to induce a positive signal somewhere else.

Yeast promoters are few and far between in iGEM, and non-inducible promoters are even rarer. We hope that our work will help future teams build complex logic with genetic network. After all, yeast is an ideal chassis in which to create complex behaviour, especially compared to prokaryotes.