The auxin-inducible degron (AID) system allows the rapid and reversible proteolysis of proteins of interest, which have been invented by Dr. Masato Kanemaki in National Institute of Genetics in Japan. OsTIR1 is a F-box family protein specifically expressed in a rice plant. Since OsTIR1 can function under a culture condition at 37 degree, it is integrated in the AID system to work it in mammalian cells. Briefly, OsTIR1 binds to endogenous Skp1 to form the Skp1-Cullin1-OsTIR1 complex (SCF^TIR1). SCF^TIR1 binds and ubiquitinates the AID tag in the presence of auxin, and promotes proteasome-dependent degradation of the AID-tagged target protein. Human HCT116 cell lines harboring OsTIR1 (CMV-OsTIR1 RCB4662 or Tet-OsTIR1) are available from the RIKEN Cell Bank.