The present invention relates to a system comprising a genetic construct a riboswitch operably linked to a regulatory sequence, and a second genetic construct a coding sequence whose expression is capable of being regulated by a gene product of the first construct. Also provided is a genetic construct comprising one or more riboswitches for regulation of gene expression, wherein preferably a spacer sequence is provided downstream of the riboswitch to enhance expression of a coding sequence which is operably linked to a riboswitch. Ligands, kits, methods, host cells and expression systems are also provided.