Abstract
Feedback regulation plays a crucial role in dynamic gene expression in nature, but synthetic translational feedback systems have yet to be demonstrated. Here we use an RNA/protein interaction-based synthetic translational switch to create a feedback system that tightly controls the expression of proteins of interest in mammalian cells. Feedback is mediated by modified ribosomal L7Ae proteins, which bind a set of RNA motifs with a range of affinities. We designed these motifs into L7Ae-encoding mRNA. Newly translated L7Ae binds its own mRNA, inhibiting further translation. This inhibition tightly feedback-regulates the concentration of L7Ae and any fusion partner of interest. A mathematical model predicts system behavior as a function of RNA/protein affinity. We further demonstrate that the L7Ae protein can simultaneously and tunably regulate the expression of multiple proteins of interest by binding RNA control motifs built into each mRNA, allowing control over the coordinated expression of protein networks.