Yeast as source of oncoproteins

The properties of a Saccharomyces cerevisiae 20 kDa polypeptide (Yp20) and its relationship to human ras antigen were tested. Yp20 was isolated from commercial yeast cells by the procedure of Sommer (1978). Proteins associated with yeast chromatin were released by micrococcal nuclease digestion and purified by sucrose gradient centrifugation. Rabbit polyclonal and mouse monoclonal antibodies specifically detecting the Yp20 antigen have been generated. We observed that Yp20 was recognized by anti-ras polyclonal and monoclonal antibodies. Mammalian Ha-ras and Ki-ras proteins were specifically detected by anti-Yp20 antibodies. Based on immunological cross-reactivities, we believe that Yp20 may share some homology with the yeast YP2 gene previously described. Anti-Yp20 antibodies will be used to isolate the gene that encodes the protein. Practical applications of our antibodies for the detection of tumor specific antigens will be discussed.