Recently, the development of inducible expression systems has involved exploitation of the p-cym operon from Pseudomonas putida. Disclosed herein are novel expression systems and components thereof, which involve the development of a CymR variant with reverse DNA binding activity, such that they exhibit increased affinity for DNA in a presence rather than an absence of an effector molecule such as cumene or an equivalent thereof. Also disclosed are the CymR variant, fusion proteins incorporating such a variant, and its use in the control and expression of polynucleotides. The CymR variant comprises a 142Glu to 142Gly single point mutation of wild type CymR.