The lexA entry in FlyBase represents sequence from the Escherichia coli lexA repressor (UniProtKB:P0A7C2) that includes the DNA-binding domain, where it is known that the lexA sequence has not been fused to a transcriptional activation domain. lexA binds specifically to the lexAop DNA sequence (reviewed in PMID:18726173). If a protein of interest is tagged with lexA, then that protein can be 'tethered' to copies of lexAop that have been inserted into the genome. This property can be used to study the effect of the tagged protein of interest on chromosome organization and/or gene expression. The exact sequence of lexA may differ depending on the particular transgene or modified endogenous locus being used, for example, the coding sequence may have been codon optimized for use in different species.