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 CymR variants 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 variants, fusion proteins incorporating such variants, and their use in the control and expression of polynucleotides.