The tetO tetracycline operator DNA sequence is specifically bound by the DNA-binding domain of the tetracycline repressor (tetR) gene of the transposon Tn10-encoded operon of Escherichia coli. 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 tetO sequences can be combined with a transgene or modified endogenous locus encoding any 'driver' that includes the tetR DNA-binding domain plus a transcriptional activation sequence (PMID:1319065, PMID:9251018).