Harnessing CRISPRi Competition to Develop Multimodule Controllers for Resource-Aware Circuit Design.

Cellular resource limitations give rise to resource competition, undermining the modularity and predictability of engineered genetic circuits. In systems containing positive feedback, such competition can drive Winner-Takes-All (WTA) dynamics, resulting in severe imbalances in resource allocation across circuit modules. In this chapter, we present an experimental implementation of a Negatively Competitive Regulatory (NCR) controller based on CRISPR interference (CRISPRi) in dual self-activation (DSA) circuits. We describe a detailed workflow for chromosomal integration of a tunable dCas9 expression cassette, as well as the design of self-activation modules and module-specific guide RNAs that induce self-repression through competition for limiting dCas9. This architecture introduces effective negative feedback to the more active module while reallocating resources to the less active one, thereby promoting balanced module activity. Finally, we provide guidelines for quantitatively assessing the regulation of resource competition between DSA modules using the NCR strategy. Overall, these guidelines demonstrate how CRISPRi can be leveraged to implement NCR strategy in gene circuits, thereby enhancing circuit modularity and predictability.