Purification and Cell-free Synthesis of a Major Protein from Rat Seminal Vesicle Secretion

We have examined the protein components of Sprague-Dawley rat seminal vesicle secretion (SVS) under denaturing conditions by sodium dodecyl sulfatepolyacrylamide gel electrophoresis. Five major components are consistently resolved, which we have referred to as SVS I to SVS V in order of increasing mobility. SVS I to SVS III are relatively insoluble under physiological conditions, but this is not the case for SVS IV and SVS V. When 23-day-old rats were treated with 0.1 mg of testosterone propionate/day for 6 days, a striking induction of the synthesis or accumulation, or both, of SVS IV and SVS V occurred, whereas these proteins remained undetectable in control animals of identical age. Accordingly, these proteins should be highly useful for markers of androgen action, and we have arbitrarily chosen SVS IV to study further. SVS IV was purified by a combination of ammonium sulfate fractionation, ion exchange chromatography, and gel filtration to yield a product that appeared homogeneous in several polyacrylamide gel electrophoretie systems. The purified protein lacks tryptophan, cyst(e)ine, and common carbohydrates. Its molecular weight, estimated by electrophoretic mobility under denaturing conditions and by gel filtration, is on the order of 15,000 to 18,000. Antibody to SVS IV was raised in rabbits and used to construct an immunoaffinity column for isolation of SVS IV. Polyadenylated RNA from mature seminal vesicles was translated in a cell-free system derived from wheat germ. About 20% of the [%]methionine incorporated into total acid-precipitable material was selectively bound by anti-SVS IV antibody. The cell-free translation product that was immunologically precipitated was found to migrate more slowly during sodium dodecyl sulfate-polyacrylamide gel electrophoresis than the secreted form of SVS IV. However, the cell-free translation product was shown to give rise to the same pattern of fragments after digestion with S. aureus VS protease as the secreted form of SVS IV. It appears likely that SVS IV, like many other secreted proteins, is synthesized initially in a precursor form.