Recent studies have just started to explore the possibility of utilizing existing recombination systems that flip segments of DNA to store information and perform computations. However, the only systems studied so far are not completely unidirectonal in their ability to flip a segment of DNA. Other systems studied to date have consisted of one unidirectional recombinase capable of flipping a segment of DNA in only one direction, but have lacked a complementary unidrectional recombinase to flip the DNA back in only the opposite direction. Instead, previous systems have relied on “recombination directionality factors” which when complexed with the unidirectional recombinase, reverse the direction in which it flips the DNA segment. The fim system from E. coli has been shown to contain 2 unidirectional recombinases, hbif and fime, which flip a promoter-containing segment of DNA. Our project seeks to engineer the fim switch by replacing the native promoter with another promoter. We plan to demonstrate that it can function as a reliable and efficient biological transistor, or “transcriptor”. Beyond storing information and performing basic computations, the system would serve as a very useful, tightly controlled switch.