Purification, from cultured human choriocarcinoma cells, of a 75000-Mr protein reacting with antibodies to a synthetic peptide based on a cloned human endogenous provirus nucleotide sequence.

We previously detected in cultured choriocarcinoma cells a 75000-Mr polypeptide defined by immunoblotting with antibody to a synthetic peptide Sp23 (Cys-Glu-Asn-Pro-Ser-Gln-Phe-Tyr-Glu-Asp-Leu) based on a cloned human endogenous proviral nucleotide sequence. On immunohistological staining, anti-Sp23 stains antigen(s) in the syncytiotrophoblasts of first-trimester placentas and in renal-cell adenocarcinoma tissues. The present report describes purification to homogeneity of the protein from cultured choriocarcinoma cells. The procedure involves extraction with non-ionic detergent and h.p.l.c. using, sequentially, gel-permeation, anion-exchange and reverse-phase columns. The yield was 110 micrograms/g of total choriocarcinoma-cell protein. The results indicate that the purified protein is a monomeric and relatively hydrophilic molecule of Mr 75000.