Riboswitches: from ancient gene-control systems to modern drug targets.

Running an efficient metabolism requires finely tuned regulatory systems to make sure that the correct metabolites are produced at the necessary times and in the appropriate concentrations. To achieve this, cells make use of numerous molecular sensors and switches to control the production and function of enzymes. Interestingly, not all small-molecule sensors are made of proteins. Many bacteria and some species of archaea and eukarya are known to make use of metabolite-binding gene control elements made of RNA, called riboswitches [1, 2]. These RNAs are nature’s versions of small-molecule-binding aptamers, which are engineered RNAs created using methods first described by Larry Gold [3] and Jack Szostak [4] in the early 1990s. Most riboswitches reside in where they form selective binding pockets or aptamers for their target metabolites without the requirement for protein factors. Folding changes brought about by RNA-metabolite complex subsequently modulate the level of expression of a protein coding region usually located immediately downstream. At least 20 classes