Team:BrownTwo/Limiter/intro

Intro, including history of electronic limiter, threshold regulation

Limiter of the good ol' days

n the early days of radio, AM transmitters were vulnerable to overload by an input signal of too great a magnitude. To protect the transmitter from damage, a limiter circuit was employed to attenuate signal peaks while allowing all subthreshold signal to pass through unchanged. We have designed a genetic circuit that behaves similarly. Our gene network reacts to the level of transcription of a gene of interest, limiting it to levels above or below a user-defined threshold. In our proof-of-concept, we use synthetic transcription factors to limit the expression of an inducible reporter. In practice, these modular transcription factors can be used to regulate any endogenous gene with a known promoter and transcription factor DNA-binding domain. Extremes of gene expression can damage living systems, while normal expression is healthy. Our limiter could react to the level of a gene's expression within individual cells, correcting problems only where they occur.

Our limiter device represents an example of a complex device built from smaller parts and circuits available to synthetic biology. At the same time, however, it also constitutes a departure from the iGEM tradition of building devices that function solely in a bacterial chassis.