The cymO operator DNA sequence is specifically bound by the DNA-binding domain of the cymR gene of Pseudomonas putida. This property can be utilized to form a binary expression system to control the spatial and temporal expression of a gene of interest: a transgene or modified endogenous locus in which the target gene of interest is downstream of cymO sequences can be combined with a transgene or modified endogenous locus encoding any 'driver' that includes the cymR DNA-binding domain plus a transcriptional activation sequence (PMID:17083727).