OsTIR1(F74G) Expression Controls Basal and Auxin-Induced Degradation Rates of the AID System in Yeast

The auxin-inducible degron (AID) system is widely used to conditionally deplete proteins in yeast, where the plant hormone auxin promotes OsTIR1-mediated degradation of AID-tagged proteins. However, “basal” degradation of AID-tagged proteins in the absence of auxin has hampered work with essential proteins, leading to defective or non-viable strains. A second-generation AID system based on the OsTIR1(F74G) mutant was introduced to overcome this limitation, yet the extent to which it eliminates basal degradation and affects auxin-induced degradation remained unclear. Here, we quantitatively characterize basal and auxin-induced degradation dynamics using OsTIR1(F74G) in budding yeast. We find that basal degradation remains detectable and depends on OsTIR1(F74G) expression levels. Auxin-induced degradation rates and steady-state concentrations of AID-tagged proteins likewise depend on OsTIR1(F74G) expression levels and the type of auxin used. We further demonstrate that elevated basal degradation of functional AID-tagged proteins can impair cell growth and lead to unwanted phenotypes. Our findings will guide future applications of the AID system by helping researchers select appropriate OsTIR1(F74G) expression levels, particularly when precise control of degradation dynamics is required.