Widely used in the electric world, the electromagnetic relay is acting as the pivot of a working circuit and a control circuit so that it is the key component of electrical automatic control system. When the output signal reaches the threshold intensity, the relay will shift it state, resulting in the change of ON/OFF condition of a separated working module. The working voltage and control voltage are relatively independent, so that it readily decouples the operational system from the control system. A common example of the relay’s utilization is the air switch. This property facilitates the exertion of devices and enhances safety for electricity use.
In biological field, relatively separable but interdependent expression systems are not yet efficiently connected. There is an imperative need of a device similar to relay when designing the genetic circuit. That is, we can solve the problem of the inconsistency of input signal intensity and reporting signal intensity—moderate concentration of product which is directly produced by operational circuit can be used to trigger the report circuit that gives a stronger yield—by applying biological relay. In addition, we are able to achieve special constructions like the self-locking switch. Instead of continuously inducing the promoter with signal input, we can induce the control circuit for once and thus leads to an irreversible state transformation in the working circuit which will constantly express itself.
Taking example by engineering science, and also inspired by 2017 team Peking, who developed a framework of programmable computational sequential circuits as modular building blocks, we use phage integrase systems and unidirectional terminator elements to construct a set of biological relay module analogous to electromagnetic relay, having a control signal input interface, a normally open contract and a normally close contract likewise. The input concentration is positively correlated to the yield of recombinase, which alters the sequence configuration and thereby opens the expression of the output circuit. It is thus possible to enable various switch function. Besides, the response performance property of the module is also modelled and quantitatively characterized by reference to the performance parameters of the electronic relay, so that those devices can be predictably adapted to different genetic circuits.
To demonstrate our biological relays, we designed and constructed a resolution extensible analog-digital converter (ADC), which can convert the consecutive analog quantities (the strength of an inducible promoter) into discrete digital signals (indicated by different chromoproteins) and thus allows the digitized processing and storage of signals. By adjusting the sequence of ribosome, we anticipate fitting curves of recombinases with different intensities and create a database, from which people can choose the proper set of a ribosome-recombinase to use. We believe that with this set of biological relay devices, we can avoid spending vast time to adjust the system in full-scale and and can get the appropriate component that meets their requirement directly. Thus, it can assist the modular design of sophisticated biological circuits, boosting the designing efficiency of artificial biological system.
Team:GENAS China/Description
