Engineered riboswitches: overview, problems and trends.

The first conditional gene expression system which employed a small molecule binding aptamer was developed several years before the discovery of natural riboswitches. With the discovery of riboswitches it became obvious that nature uses exactly the same principal of direct RNA-ligand interaction to regulate gene expression in a highly efficient, precise and fast way. In the last decade, further engineered riboswitches have been developed to control gene expression in different organisms. The successful development of new engineered riboswitches, however, is not only dependent on an innovative design but also necessitates a two step process: first, an in vitro selection which results in aptamers with high affinity binding to a desired ligand and second, a subsequent screen to identify RNAs with a desired functionality within cells. This review will give an overview of recent reports of engineered riboswitches, highlight recent developments and point out trends and problems in the field.