Synthetic biology with RNA: progress report.

One of the long-term goals in synthetic biology is the construction of large-scale gene networks to control and manipulate cells. Such networks often tweak natural regulatory mechanisms, or 'switches', in order to achieve the desired function. Regulatory mechanisms that involve RNA building blocks such as messenger RNA, microRNA and riboswitches have become increasingly prominent in this regard. Recent achievements include prototype mRNA sensors, logic circuits that respond to small molecule cues to affect cell fate, and cell-state classifier networks that identify physiological states using multiple microRNA inputs. This Review describes these and other results in RNA-based synthetic biology.