Human progesterone receptor (PR) is a member of the nuclear hormone receptor superfamily of transcriptional activators, which share a common modular structure consisting of a C-terminal ligand-binding domain (LBD), a highly conserved and centrally located DNA-binding domain (DBD), and a poorly characterized N-terminal domain that is required for maximal transcriptional activity (1 ,2 ) Human PR is expressed as two proteins from a single gene by alternate use of two promoters: PR-A, which is missing the first 164 amino acids in the N-terminus, and full-length PR-B (3 ).
