Fig. 1: Schematic of RNA-IN/RNA-OUT genetic circuits.
From: High-resolution and programmable RNA-IN and RNA-OUT genetic circuit in living mammalian cells

Three indispensable components comprise an RNA-IN/RNA-OUT circuit: 1) a programmable RNA sensor for detecting any input RNAs as RNA-IN module; 2) a programmable actuator for activating desired output-RNAs as RNA-OUT module; 3) a signal processor for linking the sensor to actuator modules.