The lexA::PR driver encodes a ligand-inducible transcriptional activator designed for use in a binary expression system. It is composed of the DNA-binding domain from the Escherichia coli lexA gene (ECOGENE:EG10533), a truncated ligand-binding domain from the Homo sapiens progesterone receptor (PGR, HGNC:8910) and the transcriptional activation domain from the Homo sapiens RELA gene (HGNC:9955). The lexA DNA-binding domain of the lexA::PR driver can bind specifically to the lexAop DNA sequence, but the presence of the PGR ligand-binding domain means that this binding, and subsequent transcriptional activation, can only occur in the presence of the anti-progestin mifepristone (RU486) (PMID:9892637).