(a) Characterization of the estrogen receptor gene and protein. ERα and ERβ are encoded by two distinct genes; the ERα gene is localized to chromosome 6q24–27; the ERβ gene is located on chromosome 14q21-22. The gene transcripts are composed of 9 exons. The two encoded proteins differ in number of amino acids with ERα being slightly longer, 595 versus 530. Both proteins have five distinct domains, three of which have relative degrees of homology. The domain with the greatest disparity resides in the A/B domain, which may account for many of the antagonistic actions observed between the two ERs. (b) Characterization of the androgen receptor gene and protein. The human androgen receptor gene is situated on the long arm of the X-chromosome, q11-12. The organization of the protein coding region is similar to that of the estrogen receptor but is divided over 8 exons. The sequence encoding the N-terminal domain (NTD) is found in exon 1. Similar to the ER, the functionality of the DNA-binding domain (DBD) is provided by a motif comprised of two zinc fingers (UU) encoded by exons 2 and 3. The first zinc finger mediates DNA recognition while the second mediates DNA-dependent dimerization. Message for the ligand-binding domain (LBD) is distributed over the remaining five exons.
