Isolation, properties, and androgen regulation of a 20-kilodalton protein from rat ventral prostate.

An abundant 20-kilodalton protein has been isolated from the cytosol fraction of rat ventral prostate by ammonium sulfate precipitation, DNA-cellulose chromatography, and gel filtration. The purified 20K protein is a glycoprotein, containing 11% hexose by weight. It contains no fucose, hexosamine, or sialic acid. The 20K protein does not bind androgen. Binding of the 20K protein to DNA is nonspecific, showing affinity toward DNAs of various tissue origins, as well as poly(dA-dT), poly(rI-rC), and phosphocellulose. The 20K protein comprises about 9% of the total cytosolic proteins in rat ventral prostate. Examination of eight different rat organs, including prostate secretion, lateral and dorsal prostates, and rat ejaculate, for the presence of the 20K protein by double immunodiffusion analysis revealed that the protein is a rat ventral prostate specific secretory protein. Hybridization of prostatic poly(A) RNA with a cloned cDNA coding for the 20K protein indicated that the synthesis of the 20K protein is regulated by testosterone at the mRNA level.