The lexA::QF entry in FlyBase represents an artificial transcriptional activator ('driver') that includes the DNA-binding domain from the Escherichia coli lexA gene (ECOGENE:EG10533) and the transcriptional activation domain of Neurospora crassa QA-1F (UniProtKB:P11638). 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::QF protein is converted into a transcriptional activator that specifically binds lexAop. lexAop and lexA::QF 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::QF driver. The exact sequence of the driver may differ depending on the particular transgene or modified endogenous locus being used. For example, while a nuclear localization signal must be present in the driver, this may be derived from the lexA gene or another source. In addition, the QA-1F activation domain may contain mutation(s) that alter its activity, changing the strength of an individual driver. Since the lexA::QF driver includes the QA-1F activation domain targeted by the QS repressor, it can be suppressed by QS (FBrf0227669).