Figure 1.

Schematic representation of modular assembly and mechanism of an RNA control device based on a ribozyme actuator. Ribozyme-based devices are constructed by modular assembly of three functional RNA components. A sensor (RNA aptamer) is linked to an actuator (hammerhead ribozyme) through a distinct information transmitter sequence (which directs a strand-displacement event and insulates the sensor and actuator components). Ribozyme-based devices are integrated into the 3′ untranslated region of the target gene and can adopt at least two functional device conformations, where each conformation is associated with different actuator and sensor activities. In the depicted example, a ribozyme ON device (upregulation of gene expression in response to increased input ligand concentration) adopts a ribozyme-active conformation associated with an aptamer ligand-unbound state, where ribozyme cleavage results in an unprotected transcript that is subject to rapid degradation by ribonucleases, thereby leading to a decrease in gene expression. The ribozyme-inactive conformation is associated with an aptamer ligand-bound state, such that ligand binding to the aptamer stabilizes the ribozyme-inactive conformation, thereby leading to an increase in gene expression in response to ligand.