Used in yeast cell culture, particularly in Saccharomyces cerevisiae studies, to support selection and maintenance of plasmids lacking tryptophan and uracil biosynthetic markers. This supplement is added to defined media to enable growth of auxotrophic strains engineered for genetic experiments such as two-hybrid screening, plasmid transformation, and gene expression analysis. By omitting tryptophan and uracil, only cells retaining the corresponding complementing genes on plasmids can grow, allowing researchers to maintain selective pressure and monitor gene function or protein interactions effectively.