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.