Difference between revisions of "Team:William and Mary/Description"

The inherent versatility of synthetic genetic circuitry has lead to a vast array of diverse applications in countless fields. However, the field remains fundamentally limited by the magnitude and specificity of behavioral control over genetic circuits and circuit networks. These limitations can be boiled down to two essential problems: inherent constraints to behavior based on the nature of a circuit’s constituent genes, and the inefficiency of the “design-build-test” cycle which is relied upon for the construction of effective circuit models.

The fundamental constraints of integral circuit components limit the ability to design and construct genetic circuits of arbitrary and highly specific behavior. When constructing a circuit with some intended behavior, design is limited by the available input-specific regulators to gene expression and their characteristic regulatory behavior. In order to achieve more precise behavioral control, the ability to tune expression levels of regulatory elements to some desired level is vital. This limitation highlights the need for genetic devices that can modify the behavior of arbitrary genetic circuits; implementing these devices would enable precise behavioral control invariant to the constraints of the constituent genes that make up the circuit in question [1].

The other foundational limitation of genetic circuit construction addresses the inefficiency and unpredictability of the design and construction process itself. The progression from synthesizing parts into a circuit on a plasmid, to transformation and testing in vivo, is a lengthy and expensive process which furthermore is largely variable in terms of actual functionality of the final product [2].This often leads to a series of trial-and-error testing cycles whose products maintain a persistent level of uncertainty with regard to precise, predictable behavior. Although it is possible to achieve functional genetic circuits in this capacity, greater problems arise regarding the tunability of the product. The success of any genetic circuit relies on the ability to precisely tune a response to a range of input concentrations; it would therefore be desirable to obtain a reliable method for tuning circuit response, ideally without the need to rewire the internal workings of the circuit. This method would allow control over output expression to be implemented in a more rapid and predictable manner [3].

The overall input/output behavior of any genetic circuit can be represented by a graph known as a transfer function, which relates concentration of input molecule to output protein expression. Likewise, any modifications to the circuit affecting input/output behavior can be visualized by a transformation of the transfer function representing the circuit. The Circuit Control Toolbox consists of three distinct tools which prompt unique behavioral changes to the circuit’s output relative to its input, and therefore generate different transformations of the circuit’s original transfer function.

The RBS library [link to page] provides a collection of ribosome binding sites of varying strength; replacing the RBS within a circuit alters the translational efficiency of the output. This tool effectively allows for scaled changes in the magnitude of a circuit’s output response, thus adjusting the amplitude of the transfer function.

The Decoy Binding Array [link to page] tool implements molecular titration to tune the circuit’s sensitivity to input concentrations. This modification is accompanied by a shift in the threshold of the circuit’s transfer function.

The Synthetic Enhancer Suite [link to page] exploits a synthetically modified enhancer/promoter system engineered to allow genetic circuits to generate multi-state responses. In other words, circuits are prompted to produce distinct levels of output based on the concentration of input molecule. This creates a staircase-like curve in the transfer function for the circuit.

Each of these tools functions orthogonally to the activity of the other tools; furthermore, each tool is independently tunable to a specific degree. By implementing and adjusting multiple tools to the desired degree, a diverse range of circuit output behaviors can be achieved, generating a plethora of unique transfer function responses.