plants have evolved a unique system in which the plant hormone auxin directly induces rapid degradation of the aux iaa family of transcription repressors by a specific form of the scf e3 ubiquitin ligase other eukaryotes lack the auxin response but share the scf degradation pathway allowing us to transplant the auxin inducible degron aid system into nonplant cells and use a small molecule to conditionally control protein stability the aid system allowed rapid and reversible degradation of target proteins in response to auxin and enabled us to generate efficient conditional mutants of essential proteins in yeast as well as cell lines derived from chicken mouse hamster monkey and human cells thus offering a powerful tool to control protein expression and study protein function.