A 20-kDa protein in human seminal plasma that is identical to gross cystic disease fluid protein 15 and prolactin-inducible protein.

A new method is described for isolating the 20-kDa protein, which used to be purified using an actin-immobilized column from human seminal plasma. This method employed ion-exchange column chromatography and isoelectric focusing separation. The level of seminal protein was determined by sandwich ELISA to be 1.06 +/- 0.27 mg/mL (mean +/- SD, n = 8). Its cDNA was cloned from a human salivary gland cDNA library by immunoscreening. The 553-nucleotide sequence included the 5' untranslated region and extended to the poly(A) tail. It encoded a protein of 118 amino acid residues in addition to a signal sequence of 28 residues. This sequence was identical to those of gross cystic disease fluid protein 15 and prolactin-inducible protein cDNAs. Northern blotting revealed the common expression in the submandibular gland and seminal vesicle. An immunohistochemical study in paraffin-embedded tissues from human male sex organs also indicated that the 20-kDa protein is mainly produced in the seminal vesicle.