Used as a selective agent in cell culture to kill cells that do not express resistance genes, commonly applied in stable cell line development. Enables selection in both bacterial and mammalian systems when paired with a resistance gene. Widely used in molecular biology for screening transfected or transduced cells. Also inhibits protein synthesis by mimicking tRNA, making it a tool for studying translation mechanisms. Effective in vivo and in vitro, with applications in cancer research and gene expression studies.