Since the discovery of transcription attenuation as a mechanism of bacterial gene regulation, a broad variety of attenuation mechanisms have been unveiled and analysed. In 2002, the first convincing experimental evidence for metabolite-mediated attenuation, termed riboswitch, was published. Subsequently, riboswitches have been found to be widespread among bacteria and are also used in some eukaryotes. A surprising new finding has been a riboswitch acting as a metabolite-responsive ribozyme - the first new naturally occurring ribozyme discovered since 1990.