Chang EC et al. - Our observations indicate that genistein is a potency-selective ligand for gene expression regulation by ER alpha and ER beta and that the ability of ER alpha and ER beta to serve as determinants of gene expression is greatly influenced by the nature of the ligand, by ligand dose, and by the differential abilities of ligand-ER complexes to recruit different coregulators at ER binding sites of hormone-regulated genes.