The lexA::p65 entry in FlyBase represents an artificial transcriptional activator ('driver') that includes the DNA-binding domain from the Escherichia coli lexA gene (ECOGENE:EG10533) and a transcriptional activation domain from the Homo sapiens 'p65' gene (RELA, HGNC:9955). The exact sequence of the driver may differ depending on the particular transgene or modified endogenous locus being used. In Escherichia coli the lexA protein acts as a transcriptional repressor, binding specifically to the lexAop DNA sequence via its DNA-binding domain (reviewed in PMID:18726173). By fusing the lexA DNA-binding domain to a transcriptional activation domain, the resulting lexA::p65 protein is converted into a transcriptional activator that specifically binds lexAop. lexAop and lexA::p65 thus form a binary expression system that can be used to control the spatial and temporal expression of a gene of interest: a transgene or modified endogenous locus carrying the target gene of interest downstream of lexAop sequences is combined with a second transgene or modified endogenous locus encoding the lexA::p65 driver (FBrf0212052).