The lexA::GAD 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 Saccharomyces cerevisiae GAL4 gene ( SGDID:S000006169 ). 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::GAD protein is converted into a transcriptional activator that specifically binds lexAop. lexAop and lexA::GAD 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::GAD driver. The exact sequence of the driver may differ depending on the particular transgene or modified endogenous locus being used. In particular, GAL4 contains two separate regions that can each activate transcription when fused with a DNA-binding domain: activation domain I (amino acid residues 148-196) and the C-terminal activation domain II (amino acid residues 768-881) (PMID:3028647). Some lexA::GAD drivers contain only activation domain II (FBrf0191281) while others contain an extended GAL4 sequence that includes both activation domains, resulting in a stronger driver (FBrf0212052, FBrf0211848). In addition, since the lexA::GAD driver includes the C-terminal GAL4 sequence targeted by the GAL80 suppressor, it can be suppressed by GAL80 (FBrf0191281).