This part serves as a key structure in our scheme. This plasmid expresses a small RNA that can specifically bind to the secondary structure of the corresponding stem loop and resolve its structure, which allows the DNA sequence downstream the stem loop to be transcribed.

This part serves as a lock structure in our scheme, in which EGFP is used as a substitute for our encrypted information, and can be used to verify the function of our lock part. Thus, only when a specific small RNA binds to the stem loop and changes the stem loop secondary structure, EGFP transcription can be initiated and EGFP expression can be achieved. This unit contains six parts: the CYC promoter, STEMLOOP, EGFP coding sequence, the CYC terminator and homology arms HA1 and HA2. HA1 and HA2 act as homology arms to achieve homologous recombination, which can insert the DNA with the lock structure sequence into the yeast genome. The stemloop acts as a lock to protect our encrypted information to be transmitted.

This plasmid allows a-type yeast to sense the pheromone α factor secreted by α-type yeast. The a-type Saccharomyces cerevisiae expresses Bax protein, which can arrest cell cycle and reduce cell density. Therefore, upon induction by α factor the a-type yeast cells carrying this plasmid undergo a decrease in cell density, which can be used to protect our encrypted information.