The ttgO operator DNA sequence is specifically bound by the DNA-binding domain of the ttgR 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 ttgO sequences can be combined with a transgene or modified endogenous locus encoding any 'driver' that includes the ttgR DNA-binding domain plus a transcriptional activation sequence (PMID:19549857).