This study examines the history of yeast hereditary research out of the fermentation industries and into the genetics laboratory, where a single-celled fungus underwent material, technical, and conceptual transformations to become an experimental system, an ideal eukaryotic cell, a model organism, and a genetically-engineered cell factory with which to advance the molecularization of human health and disease. The work draws from new and existing oral histories and archives across academic and commercial institutions to follow the development, circulation, and use of Saccharomyces cerevisiae wild-type yeast strain S288C and its mutants along with their accompanying experimental practices and politics in a range of international settings. The rise of the yeast model organism in U.S. biomedical research is shown to have been a political application of eukaryotic molecular biology with particular utility, for example, in accessing basic science funding for cancer research at the level of the cell. A final case study of yeast-made recombinant Hepatitis B vaccine reveals how the biotech industry manufactured therapeutics out of human molecules on the rise of eukaryotic molecular biology.