An Estrogen-Binding Protein and Endogenous Ligand in Saccharomyces cerevisiae : Possible Hormone Receptor System

A protein macromolecule in the cytosol of the unicellular eukaryotic yeast Saccharomyces cerevisiae selectively binds the vertebrate estrogen hormone 17 beta-estradiol with high affinity. Lipid extracts of the yeast cells or the conditioned growth medium yield a substance that can bind competitively to the tritiated estradiol-binding sites in the yeast and to mammalian estrogen receptors. These findings suggest that the binding protein may be a primitive hormone receptor and that the lipid-extractable substance represents the endogenous ligand.